Empty string: Difference between revisions
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dim s as string |
dim s as string |
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' assign an empty string to a variable: |
' assign an empty string to a variable (six bytes): |
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s = "" |
s = "" |
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' assign null string pointer to a variable (zero bytes, according to RubberduckVBA): |
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s = vbNullString |
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' if your VBA code interacts with non-VBA code, this difference may become significant! |
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' test if a string is empty: |
' test if a string is empty: |
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Revision as of 21:29, 21 May 2020
You are encouraged to solve this task according to the task description, using any language you may know.
Languages may have features for dealing specifically with empty strings (those containing no characters).
- Task
-
- Demonstrate how to assign an empty string to a variable.
- Demonstrate how to check that a string is empty.
- Demonstrate how to check that a string is not empty.
11l
<lang 11l>V s = ‘’ I s.empty
print(‘String s is empty.’)
I !s.empty
print(‘String s is not empty.’)</lang>
8th
Assign an empty string to a variable: <lang Forth>"" var, str</lang>
Check that the string is empty: <lang Forth>str @ s:len 0 n:= if ... then</lang>
The check for a non-empty string is the same, but with "not" after the n:=
AArch64 Assembly
Declare an empty string at address str:
<lang ARM_Assembly>str: .asciz ""</lang>
Check if a string stored at x0 is empty:
<lang ARM_Assembly> mov x5, #0 ldrb w5, [x0] cmp x5, #0</lang>
Full program demo:
<lang ARM_Assembly>.equ STDOUT, 1 .equ SVC_WRITE, 64 .equ SVC_EXIT, 93
.text .global _start
_start: stp x29, x30, [sp, -16]! ldr x0, =str1 mov x29, sp bl str_empty // str_empty(""); ldr x0, =str2 bl str_empty // str_empty("non-empty"); ldp x29, x30, [sp], 16 mov x0, #0 b _exit
str1: .asciz "" str2: .asciz "non-empty" .align 4
// void str_empty(const char *s) - print "String is empty" if s is empty, "String is not empty" otherwise str_empty: mov x5, #0 ldrb w5, [x0] ldr x1, =msg_empty ldr x3, =msg_not_empty mov x2, #16 mov x4, #20 cmp x5, #0 csel x1, x1, x3, eq // msg = s[0] == 0 ? msg_empty : msg_not_empty; csel x2, x2, x4, eq // len = s[0] == 0 ? 16 : 20; mov x0, #STDOUT b _write // write(stdout, msg, len);
msg_empty: .ascii "String is empty\n" msg_not_empty: .ascii "String is not empty\n" .align 4
//////////////// system call wrappers // ssize_t _write(int fd, void *buf, size_t count) _write: stp x29, x30, [sp, -16]! mov x8, #SVC_WRITE mov x29, sp svc #0 ldp x29, x30, [sp], 16 ret
// void _exit(int retval) _exit: mov x8, #SVC_EXIT svc #0</lang>
ACL2
To check if a string is empty: <lang Lisp>(= (length str) 0)</lang>
Ada
<lang Ada>procedure Empty_String is
function Is_Empty(S: String) return Boolean is
begin
return S = ""; -- test that S is empty
end Is_Empty;
Empty: String := ""; -- Assign empty string XXXXX: String := "Not Empty";
begin
if (not Is_Empty(Empty)) or Is_Empty(XXXXX) then
raise Program_Error with "something went wrong very very badly!!!";
end if;
end Empty_String;</lang>
Aime
<lang aime>text s; s = ""; if (length(s) == 0) {
...
} if (length(s) != 0) {
....
}</lang>
ALGOL 68
<lang algol68># declare a string variable and assign an empty string to it # STRING s := "";
- test the string is empty #
IF s = "" THEN write( ( "s is empty", newline ) ) FI;
- test the string is not empty #
IF s /= "" THEN write( ( "s is not empty", newline ) ) FI;
- as a string is an array of characters, we could also test for emptyness by #
- checking for lower bound > upper bound #
IF LWB s > UPB s THEN write( ( "s is still empty", newline ) ) FI</lang>
Apex
<lang Apex> String.isBlank(record.txt_Field__c); --Returns true if the specified String is white space, empty (), or null; otherwise, returns false. </lang>
AppleScript
<lang AppleScript> -- assign empty string to str set str to ""
-- check if string is empty
if str is "" then
-- str is empty
end if
-- or
if id of str is {} then
-- str is empty
end if
-- or
if (count of str) is 0 then
-- str is empty
end if
-- check if string is not empty
if str is not "" then
-- string is not empty
end if
-- or
if id of str is not {} then
-- str is not empty
end if
-- or
if (count of str) is not 0 then
-- str is not empty
end if
</lang>
ARM Assembly
<lang ARM Assembly>
/* ARM assembly Raspberry PI */ /* program strEmpty.s */
/* Constantes */ .equ STDOUT, 1 @ Linux output console .equ EXIT, 1 @ Linux syscall .equ WRITE, 4 @ Linux syscall /* Initialized data */ .data szNotEmptyString: .asciz "String is not empty. \n" szEmptyString: .asciz "String is empty. \n" @ empty string szString: .asciz "" @ with zero final szString1: .asciz "A" @ with zero final
/* UnInitialized data */ .bss
/* code section */ .text .global main main: /* entry of program */
push {fp,lr} /* saves 2 registers */
@ load string ldr r1,iAdrszString ldrb r0,[r1] @ load first byte of string cmp r0,#0 @ compar with zero ? bne 1f ldr r0,iAdrszEmptyString bl affichageMess b 2f
1:
ldr r0,iAdrszNotEmptyString bl affichageMess
/* second string */ 2:
@ load string 1 ldr r1,iAdrszString1 ldrb r0,[r1] @ load first byte of string cmp r0,#0 @ compar with zero ? bne 3f ldr r0,iAdrszEmptyString bl affichageMess b 100f
3:
ldr r0,iAdrszNotEmptyString bl affichageMess b 100f
100: /* standard end of the program */
mov r0, #0 @ return code
pop {fp,lr} @restaur 2 registers
mov r7, #EXIT @ request to exit program
swi 0 @ perform the system call
iAdrszString: .int szString iAdrszString1: .int szString1 iAdrszNotEmptyString: .int szNotEmptyString iAdrszEmptyString: .int szEmptyString
/******************************************************************/ /* display text with size calculation */ /******************************************************************/ /* r0 contains the address of the message */ affichageMess:
push {fp,lr} /* save registres */
push {r0,r1,r2,r7} /* save others registers */
mov r2,#0 /* counter length */
1: /* loop length calculation */
ldrb r1,[r0,r2] /* read octet start position + index */
cmp r1,#0 /* if 0 its over */
addne r2,r2,#1 /* else add 1 in the length */
bne 1b /* and loop */
/* so here r2 contains the length of the message */
mov r1,r0 /* address message in r1 */
mov r0,#STDOUT /* code to write to the standard output Linux */
mov r7, #WRITE /* code call system "write" */
swi #0 /* call systeme */
pop {r0,r1,r2,r7} /* restaur others registers */
pop {fp,lr} /* restaur des 2 registres */
bx lr /* return */
</lang>
AutoHotkey
AutoHotkey has both "Traditional" or literal text, and "Expression" mode. This code demonstrates the task using both methods. <lang AutoHotkey>;; Traditional
- Assign an empty string
var =
- Check that a string is empty
If var =
MsgBox the var is empty
- Check that a string is not empty
If var !=
Msgbox the var is not empty
- Expression mode
- Assign an empty string
var := ""
- Check that a string is empty
If (var = "")
MsgBox the var is empty
- Check that a string is not empty
If (var != "")
Msgbox the var is not empty</lang>
Avail
The type string is defined as <character…|> (a tuple of characters), so the empty tuple and the empty string are equivalent values, and all tuple/collection methods can be used on strings.
<lang Avail>emptyStringVar : string := ""; Assert: emptyStringVar = ""; Assert: emptyStringVar = <>; Assert: emptyStringVar is empty; Assert: |emptyStringVar| = 0;</lang>
Checking that a string is _not_ empty generally isn't any more interesting, just a logical negation of the above tests.
<lang Avail>nonemptyStringVar : string := "content!"; Assert: nonemptyStringVar ≠ ""; Assert: nonemptyStringVar ≠ <>; Assert: ¬nonemptyStringVar is empty; Assert: |nonemptyStringVar| > 0;</avail>
The library also defines a type _nonempty string_, which can be leveraged for a type-membership check.
<lang Avail>Assert: nonemptyStringVar ∈ nonempty string;</lang>
AWK
<lang awk>#!/usr/bin/awk -f BEGIN {
# Demonstrate how to assign an empty string to a variable. a=""; b="XYZ"; print "a = ",a; print "b = ",b; print "length(a)=",length(a); print "length(b)=",length(b); # Demonstrate how to check that a string is empty. print "Is a empty ?",length(a)==0; print "Is a not empty ?",length(a)!=0; # Demonstrate how to check that a string is not empty. print "Is b empty ?",length(b)==0; print "Is b not empty ?",length(b)!=0;
}</lang>
- Output:
$ awk -f R/tmp/string.awk a = b = XYZ length(a)= 0 length(b)= 3 Is a empty ? 1 Is a not empty ? 0 Is b empty ? 0 Is b not empty ? 1
Axe
<lang axe>""→Str1 !If length(Str1)
Disp "EMPTY",i
Else
Disp "NOT EMPTY",i
End</lang>
BASIC
<lang basic>10 LET A$="" 20 IF A$="" THEN PRINT "THE STRING IS EMPTY" 30 IF A$<>"" THEN PRINT "THE STRING IS NOT EMPTY" 40 END</lang>
Applesoft BASIC
The terminating quote may be left off. By default, strings are initially empty so the assignment is not necessary. Another way to check for an empty string is to use the LEN function. <lang basic> 10 LET A$ = "
40 IF LEN (A$) = 0 THEN PRINT "THE STRING IS EMPTY" 50 IF LEN (A$) THEN PRINT "THE STRING IS NOT EMPTY"</lang>
BaCon
The literal empty string in BaCon is "".
<lang freebasic>' Empty string a$ = "" IF a$ = "" THEN PRINT "Empty string" IF a$ != "" THEN PRINT "Non empty string"</lang>
There are other ways, such as a zero return from the LEN(s$) or ULEN(utf$) functions. EQUAL(s$, "") would be another way.
IS-BASIC
<lang IS-BASIC>10 LET A$="" 20 IF A$="" THEN PRINT "The string is empty." 30 IF A$<>"" THEN PRINT "The string is not empty."</lang>
Batch File
<lang dos> @echo off
- set "var" as a blank string.
set var=
- check if "var" is a blank string.
if not defined var echo Var is a blank string.
- Alternatively,
if %var%@ equ @ echo Var is a blank string.
- check if "var" is not a blank string.
if defined var echo Var is defined.
- Alternatively,
if %var%@ neq @ echo Var is not a blank string. </lang>
BBC BASIC
<lang bbcbasic> REM assign an empty string to a variable:
var$ = ""
REM Check that a string is empty:
IF var$ = "" THEN PRINT "String is empty"
REM Check that a string is not empty:
IF var$ <> "" THEN PRINT "String is not empty"
</lang>
Bracmat
There are two ways to assign a string to a variable. The variant using the = operator does not evaluate the value before the assignment, the variant using the : (match) operator does. If the value is a string, there is no difference, as a string always evaluates to itself.
<lang bracmat>( :?a
& (b=)
& abra:?c
& (d=cadabra)
& !a: { a is empty string }
& !b: { b is also empty string }
& !c:~ { c is not an empty string }
& !d:~ { neither is d an empty string }
)
</lang>
Burlesque
Empty string is "" and checking for empty strings (or empty lists) can be done with the nu command.
<lang blsq> blsq ) "" "" blsq ) ""nu 1 blsq ) "a"nu 0 </lang>
C
In C the strings are char pointers. A string terminates with the null char (U+0000, '\0'), which is not considered part of the string. Thus an empty string is "\0", while a null string is a null pointer which points to nothing.
<lang C>#include <string.h>
/* ... */
/* assign an empty string */ const char *str = "";
/* to test a null string */ if (str) { ... }
/* to test if string is empty */ if (str[0] == '\0') { ... }
/* or equivalently use strlen function
strlen will seg fault on NULL pointer, so check first */
if ( (str == NULL) || (strlen(str) == 0)) { ... }
/* or compare to a known empty string, same thing. "== 0" means strings are equal */ if (strcmp(str, "") == 0) { ... } </lang>
C#
<lang csharp>using System;
class Program {
static void Main (string[] args) {
string example = string.Empty;
if (string.IsNullOrEmpty(example)) { }
if (!string.IsNullOrEmpty(example)) { }
}
}</lang>
In depth
Compiler: Roslyn C# (language version >= 6)
Note: implementation information provided in comments was obtained reflecting .NET libraries and viewing the .NET Core reference source and may not be correct or remain relevant as time passes.
<lang csharp>using System; using System.Collections.Generic;
static class Program {
// In short:
public static void Foo()
{
string s;
// Assign empty string:
s = "";
// or
s = string.Empty;
// Check for empty string only (false if s is null):
if (s != null && s.Length == 0) { }
// Check for null or empty (more idiomatic in .NET):
if (string.IsNullOrEmpty(s)) { }
}
public static void Main()
{
// Equality is somewhat convoluted in .NET.
// The methods above are the author's recommendation for each case.
// s is initialized to null. It is a variable of the System.String type that is a null reference and is not
// the empty string.
string s = null;
// Alias Console.WriteLine(bool) with a shorter name to make the demonstration code less verbose.
Action<bool> P = Console.WriteLine;
// Assign the empty string literal to s.
s = "";
// ' Assign String.Empty to s.
s = string.Empty;
// The empty string literal is the same object reference as String.Empty because of string interning, meaning the
// behavior of the two is identical.
// From this point on, "" will be used instead of String.Empty for brevity.
//#== operator (object)
// The == operator tests for reference equality when overload resolution fails to find an operator defined by
// either operand type. However, which strings are interned is a CLR implementation detail and may be unreliable
// when comparing non-empty strings. The equivalent in VB.NET would be s Is "".
// Note that there is no such operator as Object.op_Equality(Object, Object): the use of the == operator for
// types of type Object is a C# language feature.
P((object)s == "");
//#Object.ReferenceEquals(Object, Object)
// The previous line is semantically to the following, though it does not involve a method call.
P(object.ReferenceEquals(s, ""));
//#String.op_Equality(String, String)
// The equality operator of System.String is implemented as a call to String.Equals(String). Operators cannot be
// called with method syntax in C#.
P(s == "");
//#String.Equals(String, String)
// Call the static method defined on the String type, which first calls Object.ReferenceEquals and then, after
// verifying that both are strings of the same length, compares the strings character-by-character.
P(string.Equals(s, ""));
//#Object.Equals(Object, Object)
// First checks for reference equality and whether one or both of the arguments is null. It then invokes the
// instance Equals method of the left parameter.
P(object.Equals(s, ""));
//#String.Equals(String)
// The method is called with the string literal as the receiver because a NullReferenceException is thrown if s
// is null.
P("".Equals(s));
//#String.Length
// Check the Length property. The ?. (null-conditional) operator is used to avoid NullReferenceException. The Equals
// call above can also be done this way. Null propagation makes the equality operator return false if one operand
// is a Nullable<T> and does not have a value, making this result in false when s is null.
P(s?.Length == 0);
//#String.Length
// A more traditional version of the null-conditional using a guard clause.
// Both the null-conditional and this are noticeably (~4 times) faster than "".Equals(s). In general, it appears that
// for empty strings, using the length is faster than using an equality comparison.
P(s != null && s.Length == 0);
//#String.IsNullOrEmpty(String)
// Note that all of the other methods give false for null.
// A static method of System.String that returns true if the string is null or its length is zero.
P(string.IsNullOrEmpty(s));
//#System.Collections.Generic.EqualityComparer(Of String).Default.Equals(String, String)
// The EqualityComparer(Of T) class provides default implementations when an IEqualityComparer(Of T) is required.
// The implementation for String calls String.Equals(String).
P(EqualityComparer<string>.Default.Equals(s, ""));
Console.WriteLine();
// Each of the means described above, except testing for a non-empty string.
P((object)s != "");
P(!object.ReferenceEquals(s, ""));
P(s != "");
P(!string.Equals(s, ""));
P(!object.Equals(s, ""));
P(!"".Equals(s));
P(s?.Length != 0); // Still false when s is null!
P(s == null || s.Length != 0);
P(!string.IsNullOrEmpty(s));
P(!EqualityComparer<string>.Default.Equals(s, ""));
}
}</lang>
C++
<lang cpp>#include <string>
// ...
// empty string declaration
std::string str; // (default constructed) std::string str(); // (default constructor, no parameters) std::string str{}; // (default initialized) std::string str(""); // (const char[] conversion) std::string str{""}; // (const char[] initializer list)
if (str.empty()) { ... } // to test if string is empty
// we could also use the following if (str.length() == 0) { ... } if (str == "") { ... }
// make a std::string empty str.clear(); // (builtin clear function) str = ""; // replace contents with empty string str = {}; // swap contents with temp string (empty),then destruct temp
// swap with empty string
std::string tmp{}; // temp empty string str.swap(tmp); // (builtin swap function) std::swap(str, tmp); // swap contents with tmp
// create an array of empty strings
std::string s_array[100]; // 100 initialized to "" (fixed size)
std::array<std::string, 100> arr; // 100 initialized to "" (fixed size)
std::vector<std::string>(100,""); // 100 initialized to "" (variable size, 100 starting size)
// create empty string as default parameter void func( std::string& s = {} ); // {} generated default std:string instance </lang>
Caché ObjectScript
<lang Caché ObjectScript>EMPTYSTR
; Demonstrate how to assign an empty string to a variable.
set x = ""
; Demonstrate how to check that a string is empty.
; Length 0 is empty; equality/pattern check are 1=T, 0=F
write !,"Assigned x to null value. Tests: "
write !,"String length: "_$length(x)_", Equals null: "_(x = "")_", Empty pattern: "_(x?."") ; length 0 is empty
; Demonstrate how to check that a string is not empty. Same as above.
set x = " " ;assign to a space - not null
write !!,"Assigned x to a single blank space. Tests: "
write !,"String length: "_$length(x)_", Equals null: "_(x = "")_", Empty pattern: "_(x?."")
quit</lang>
- Output:
SAMPLES>do EMPTYSTR^ROSETTA
Assigned x to null value. Tests: String length: 0, Equals null: 1, Empty pattern: 1
Assigned x to a single blank space. Tests: String length: 1, Equals null: 0, Empty pattern: 0
Clojure
<lang clojure> (def x "") ;x is "globally" declared to be the empty string (let [x ""]
;x is bound to the empty string within the let )
(= x "") ;true if x is the empty string (not= x "") ;true if x is not the empty string </lang>
COBOL
<lang cobol>
IDENTIFICATION DIVISION.
PROGRAM-ID. EMPTYSTR.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 str PIC X(10).
PROCEDURE DIVISION.
Begin.
- * Assign an empty string.
INITIALIZE str.
- * Or
MOVE " " TO str.
IF (str = " ")
DISPLAY "String is empty"
ELSE
DISPLAY "String is not empty"
END-IF.
STOP RUN.
</lang>
CoffeeScript
Empty strings are mostly straightforward in CoffeeScript, but there's one gotcha.
<lang coffeescript> isEmptyString = (s) ->
# Returns true iff s is an empty string. # (This returns false for non-strings as well.) return true if s instanceof String and s.length == 0 s ==
empties = ["", , new String()] non_empties = [new String('yo'), 'foo', {}] console.log (isEmptyString(v) for v in empties) # [true, true, true] console.log (isEmptyString(v) for v in non_empties) # [false, false, false] console.log (s = ) == "" # true console.log new String() == # false, due to underlying JavaScript's distinction between objects and primitives </lang>
Common Lisp
Common Lisp treats empty strings as true (T in Common Lisp), therefore one must check the length of the string to know if it is empty or not. <lang lisp> (defparameter *s* "") ;; Binds dynamic variable *S* to the empty string "" (let ((s "")) ;; Binds the lexical variable S to the empty string ""
(= (length s) 0) ;; Check if the string is empty (> (length s) 0)) ;; Check if length of string is over 0 (that is: non-empty)
</lang>
Component Pascal
BlackBox Component Builder <lang oberon2> MODULE EmptyString; IMPORT StdLog;
PROCEDURE Do*;
VAR
s: ARRAY 64 OF CHAR;
(* s := "" <=> s[0] := 0X => s isEmpty*)
BEGIN
s := "";
StdLog.String("Is 's' empty?:> ");StdLog.Bool(s = "");StdLog.Ln;
StdLog.String("Is not 's' empty?:> ");StdLog.Bool(s # "");StdLog.Ln;
StdLog.Ln;
(* Or *)
s := 0X;
StdLog.String("Is 's' empty?:> ");StdLog.Bool(s = 0X);StdLog.Ln;
StdLog.String("Is not 's' empty?:> ");StdLog.Bool(s # 0X);StdLog.Ln;
StdLog.Ln;
END Do;
END EmptyString.
</lang>
Execute: ^Q EmptyString.Do
- Output:
Is 's' empty?:> $TRUE Is not 's' empty?:> $FALSE Is 's' empty?:> $TRUE Is not 's' empty?:> $FALSE
D
D treats null strings and empty strings as equal on the value level, but different on object level. You need to take this into account when checking for emptiness. <lang d>import std.array;
bool isEmptyNotNull(in string s) pure nothrow @safe {
return s is "";
}
void main(){
string s1 = null; string s2 = ""; // the content is the same assert(!s1.length); assert(!s2.length); assert(s1 == "" && s1 == null); assert(s2 == "" && s2 == null); assert(s1 == s2);
// but they don't point to the same memory region assert(s1 is null && s1 !is ""); assert(s2 is "" && s2 !is null); assert(s1 !is s2); assert(s1.ptr == null); assert(*s2.ptr == '\0'); // D string literals are \0 terminated assert(s1.empty); assert(s2.isEmptyNotNull());
}</lang>
Dart
<lang dart>main() {
var empty = ;
if (empty.isEmpty) {
print('it is empty');
}
if (empty.isNotEmpty) {
print('it is not empty');
}
}</lang>
Delphi
<lang Delphi>program EmptyString;
{$APPTYPE CONSOLE}
uses SysUtils;
function StringIsEmpty(const aString: string): Boolean; begin
Result := aString = ;
end;
var
s: string;
begin
s := ; Writeln(StringIsEmpty(s)); // True
s := 'abc'; Writeln(StringIsEmpty(s)); // False
end.</lang>
DWScript
<lang delphi>var s : String;
s := ; // assign an empty string (can also use "")
if s = then
PrintLn('empty');
s := 'hello';
if s <> then
PrintLn('not empty');</lang>
Dyalect
Demonstrate how to assign an empty string to a variable:
<lang dyalect>var str = ""</lang>
Demonstrate how to check that a string is empty:
<lang dyalect>if !str { } //or if str.isEmpty() { }</lang>
Demonstrate how to check that a string is not empty:
<lang dyalect>if str { } //or if !str.isEmpty() { }</lang>
Déjà Vu
Like in Python, empty strings are falsy, non-empty strings are truthy. <lang dejavu>local :e ""
if not e:
!print "an empty string"
if e:
!print "not an empty string"</lang>
EasyLang
<lang>a$ = "" if a$ = ""
print "empty"
. if a$ <> ""
print "no empty"
.</lang>
Elena
ELENA 4.x: <lang elena>import extensions;
public program() {
auto s := emptyString;
if (s.isEmpty())
{ console.printLine("'", s, "' is empty") };
if (s.isNonempty())
{ console.printLine("'", s, "' is not empty") }
}</lang>
- Output:
'' is empty
Elixir
To check whether a given variable holds an empty string, either compare it to the empty string literal, check its length - O(M), or check it's byte size - O(1)). <lang elixir> empty_string = "" not_empty_string = "a"
empty_string == ""
- => true
String.length(empty_string) == 0
- => true
byte_size(empty_string) == 0
- => true
not_empty_string == ""
- => false
String.length(not_empty_string) == 0
- => false
byte_size(not_empty_string) == 0
- => false
</lang>
Emacs Lisp
<lang Lisp>(setq str "") ;; empty string literal
(if (= 0 (length str))
(message "string is empty"))
(if (/= 0 (length str))
(message "string is not empty"))</lang>
Also possible is (string= "" str).
Erlang
<lang erlang> 1> S = "". % erlang strings are actually lists, so the empty string is the same as the empty list []. [] 2> length(S). 0 3> case S of [] -> empty; [H|T] -> not_empty end. empty 4> case "aoeu" of [] -> empty; [H|T] -> not_empty end. not_empty </lang>
Euphoria
<lang euphoria>sequence s
-- assign an empty string s = ""
-- another way to assign an empty string s = {} -- "" and {} are equivalent
if not length(s) then
-- string is empty
end if
if length(s) then
-- string is not empty
end if</lang>
F#
<lang fsharp>open System
[<EntryPoint>] let main args =
let emptyString = String.Empty // or any of the literals "" @"" """""" printfn "Is empty %A: %A" emptyString (emptyString = String.Empty) printfn "Is not empty %A: %A" emptyString (emptyString <> String.Empty) 0</lang>
- Output:
Is empty "": true Is not empty "": false
Factor
It's idiomatic in Factor to prefer using the stack over variable bindings.
<lang factor>"" empty? .</lang>
- Output:
t
However, Factor provides lexical variables:
<lang factor>USE: locals [let
"" :> empty-string empty-string empty? . empty-string empty? not .
]</lang>
- Output:
t f
Fantom
Fantom uses "" to represent an empty string, and provides the isEmpty method to check if a string is empty.
<lang fantom> a := "" // assign an empty string to 'a' a.isEmpty // method on sys::Str to check if string is empty a.size == 0 // what isEmpty actually checks a == "" // alternate check for an empty string !a.isEmpty // check that a string is not empty </lang>
Forth
Strings are represented as an addr-len pair on the stack. An empty string has len 0. <lang forth> \ string words operate on the address and count left on the stack by a string \ ? means the word returns a true/false flag on the stack
- empty? ( c-addr u -- ? ) nip 0= ;
- filled? ( c-addr u -- ? ) empty? 0= ;
- ="" ( c-addr u -- ) drop 0 ; \ It's OK to copy syntax from other languages
</lang>
Forth Console Test (True= -1, False=0)
s" This is not empty" empty? . 0 ok s" This is filled" filled? . -1 ok s" " empty? . -1 ok s" this is filled" ="" empty? . -1
Fortran
Early Fortran offered only rather strange methods of manipulating text, involving overwriting text literals within a FORMAT statement via a READ statement that used that format statement. Such text could not be inspected, whether to see if it was blank or anything else. Fortran 4 introduced the A format whereby text could be stored in integer or floating-point variables or arrays, and then those variables could be manipulated and inspected - though their numerical values would be unusual, especially if in floating-point variables. Fortran 77 introduced a CHARACTER definition which greatly eased matters but it was not a "string" type, which is to say, a variable storing some sequence of characters (or, in principle, integers, or other data) and also having a length. A variable may be declared as having a fixed size, as in CHARACTER*24 TEXT, and there is a library function LEN which for that variable would return 24, no matter what the variable contained. That is to say, it reports the size of the variable, not the length in current use of a string of up to 24 characters as would be the case for a similar declaration in for example, Pascal.
Such variables, or text literals, may be passed as a parameter to a subprogram, and it may use the LEN function to ascertain the size of the parameter, which in that sense could be considered a string because CHARACTER parameters are passed with a secret additional parameter, their size, which is available to the LEN function within the subprogram. <lang fortran> SUBROUTINE TASTE(T)
CHARACTER*(*) T !This form allows for any size.
IF (LEN(T).LE.0) WRITE(6,*) "Empty!"
IF (LEN(T).GT.0) WRITE(6,*) "Not empty!"
END
CHARACTER*24 TEXT
CALL TASTE("")
CALL TASTE("This")
TEXT = "" !Fills the entire variable with space characters.
CALL TASTE(TEXT) !Passes all 24 of them. Result is Not empty!
END</lang>
Otherwise, you could employ the Fortran protocol that trailing spaces are irrelevant in text comparisons. Thus TEXT .EQ. "" would give true even though TEXT might contain thousands of space characters, and so would TEXT .EQ. " " - thus an empty string is one containing nothing other than spaces.
Alternatively, the programmer can be diligent, and associate an integer with every such CHARACTER variable, such as LTEXT for TEXT, to hold the current length of characters in use. Tests for empty strings and the like would thus be made by inspecting the value of LTEXT, which hopefully, would always contain correct values.
With F90, compound data aggregates can be defined and as well procedures for operating on them, so that, after a great deal of syntactic struggle, a string data type will be available. F2000 standardised one such scheme whereby character variables are de-allocated and re-allocated with usage so that a statement such as TEXT = "This" // "That" would cause a de-allocation of whatever storage had been associated with TEXT followed by a re-allocation of storage for eight characters, the required size, and LEN(TEXT) would give 8.
Free Pascal
Assigning an empty string:
<lang pascal>s := ;</lang>
Checking for an empty string:
<lang pascal>s =
length(s) = 0</lang>
Checking for a non-empty string:
<lang pascal>s <>
length(s) > 0
longBool(length(s))</lang>
The sysUtils unit defines the constants emptyStr and emptyWideStr, which can be used in place of ''.
FreeBASIC
<lang freebasic>' FB 1.05.0 Win64
Sub IsEmpty(s As String)
If Len(s) = 0 Then
Print "String is empty"
Else
Print "String is not empty"
End If
End Sub
Dim s As String ' implicitly assigned an empty string IsEmpty(s) Dim t As String = "" ' explicitly assigned an empty string IsEmpty(t) Dim u As String = "not empty" IsEmpty(u) Sleep</lang>
- Output:
String is empty String is empty String is not empty
FutureBasic
FB has several ways to determine string length as demonstrated below. Note: The length -- or number of characters -- of a Pascal string in FB is stored in the first element of the string array. Here the string is dimensioned a s, hence s[0] contains the length of the string, and any individual character in the string can be found using s[i], where i is the position of the character. This makes iterating over the individual characters in a string easier than using functions such as instr or mid$. <lang futurebasic> include "ConsoleWindow"
dim as Str255 s
s = "" if s == "" then print "String is empty" if s[0] == 0 then print "String is empty" if len(s) == 0 then print "String is empty"
s = "Hello" if s <> "" then print "String not empty." if s[0] then print "String not empty." if len(s) > 0 then print "String not empty." </lang>
Gambas
Click this link to run this code <lang gambas>Public Sub Main() Dim sString As String[] = ["", "Hello", "world", "", "Today", "Tomorrow", "", "", "End!"] Dim sTemp As String Dim siCount As Short
For Each sTemp In sString
If sString[siCount] Then Print "String " & siCount & " = " & sString[siCount] Else Print "String " & siCount & " is empty" End If Inc siCount
Next
End</lang> Output:
String 0 is empty String 1 = Hello String 2 = world String 3 is empty String 4 = Today String 5 = Tomorrow String 6 is empty String 7 is empty String 8 = End!
Go
Go has no special syntax for empty strings. In Go variables are always initialized to a provided value or to the "zero value" of the type. The zero value of a string is the empty string. <lang go>// define and initialize an empty string var s string s2 := ""
// assign an empty string to a variable s = ""
// check that a string is empty, any of: s == "" len(s) == 0
// check that a string is not empty, any of: s != "" len(s) != 0 // or > 0</lang>
- <lang go>package main
import ( "fmt" )
func test(s string) { if len(s) == 0 { fmt.Println("empty") } else { fmt.Println("not empty") } }
func main() { // assign an empty string to a variable. str1 := "" str2 := " " // check if a string is empty. test(str1) // prt empty // check that a string is not empty. test(str2) // prt not empty }</lang>
Groovy
<lang groovy>def s = // or "" if you wish assert s.empty
s = '1 is the loneliest number' assert !s.empty</lang>
Haskell
<lang haskell>import Control.Monad
-- In Haskell strings are just lists (of characters), so we can use the function -- 'null', which applies to all lists. We don't want to use the length, since -- Haskell allows infinite lists.
main = do
let s = "" when (null s) (putStrLn "Empty.") when (not $ null s) (putStrLn "Not empty.")</lang>
HolyC
<lang holyc>/* assign an empty string */ U8 *str = StrNew(""); /* or */ U8 *str = "";
/* to test if string is empty */ if (StrLen(str) == 0) { ... } /* or compare to a known empty string. "== 0" means strings are equal */ if (StrCmp(str, "") == 0) { ... }
/* to test if string is not empty */ if (StrLen(str)) { ... }</lang>
i
<lang i>software { s = ""
// Can either compare the string to an empty string or // test if the length is zero. if s = "" or #s = 0 print("Empty string!") end
if s - "" or #s - 0 print("Not an empty string!") end } </lang>
Icon and Unicon
Icon and Unicon can produce empty strings in several ways: <lang Icon>s := "" # null string s := string('A'--'A') # ... converted from cset difference s := char(0)[0:0] # ... by slicing
s1 == "" # lexical comparison, could convert s1 to string s1 === "" # comparison won't force conversion
- s1 = 0 # zero length, however, *x is polymorphic
- string(s1) = 0 # zero length string
s1 ~== "" # non null strings comparisons s1 ~=== ""
- string(s1) ~= 0
s := &null # NOT a null string, null type /s # test for null type \s # test for non-null type </lang>
J
<lang j> variable=:
0=#variable
1
0<#variable
0</lang>
Note that J attempts to make no distinction between empty lists, regardless of their type. In other words, while some operations can reveal the type of an empty list (for example, anything that can introduce padding based on the type of the list itself) this distinction is ignored whenever possible. You can perform arithmetic on an empty string, and you can append text to an empty list of numbers even though these operations would not succeed on non-empty lists of the same type.
Thus it's not appropriate, in general case J code, to check that an empty string is of type string.
Note also that in an if. or while. statement, J treats an empty string (or the absence of any argument) as true.
Java
String.isEmpty() is part of Java 1.6. Other options for previous versions are noted.
<lang java5>String s = "";
if(s != null && s.isEmpty()){//optionally, instead of "s.isEmpty()": "s.length() == 0" or "s.equals("")"
System.out.println("s is empty");
}else{
System.out.println("s is not empty");
}</lang>
JavaScript
Create an empty String <lang javascript>var s = ""; var s = new String();</lang>
Boolean expressions representing emptiness <lang javascript>s == "" s.length == 0 !s !Boolean(s)</lang>
Non-emptiness <lang javascript>!!s s != "" s.length != 0 s.length > 0 Boolean(s)</lang>
jq
jq strings are JSON strings. The empty string literal is simply "". It can be assigned to a variable as illustrated by this example:<lang jq>"" as $x </lang>If s is a string or an array, then the additive "zero" for s can be created by writing s[0:0]. That is, if s is a string, then s[0:0] will yield the empty string. This is useful when writing polymorphic functions.
To determine whether a string, s, is empty:<lang jq>s == ""
- or:
s|length == 0</lang>To determine whether a string, s, is non-empty:<lang jq>s != ""
- or:
s.length != 0 # etc.</lang>
Jsish
<lang javascript>/* Empty string, in Jsish */ var em1 = ; var em2 = new String();
var str = 'non-empty';
- 'Empty string tests';
- em1 == ;
- em1 === ;
- em1.length == 0;
- !em1;
- (em1) ? false
- true;
- Object.is(em1, );
- Object.is(em1, new String());
- 'Non empty string tests';
- str != ;
- str !== ;
- str.length != 0;
- str.length > 0;
- !!str;
- (str) ? true
- false;
- 'Compare two empty strings';
- (em1 == em2);
- (em1 === em2);
/*
!EXPECTSTART!
'Empty string tests' em1 == ==> true em1 === ==> true em1.length == 0 ==> true !em1 ==> true (em1) ? false : true ==> true Object.is(em1, ) ==> true Object.is(em1, new String()) ==> true 'Non empty string tests' str != ==> true str !== ==> true str.length != 0 ==> true str.length > 0 ==> true !!str ==> true (str) ? true : false ==> true 'Compare two empty strings' (em1 == em2) ==> true (em1 === em2) ==> true
!EXPECTEND!
- /</lang>
- Output:
prompt$ jsish --U emptyString.jsi 'Empty string tests' em1 == '' ==> true em1 === '' ==> true em1.length == 0 ==> true !em1 ==> true (em1) ? false : true ==> true Object.is(em1, '') ==> true Object.is(em1, new String()) ==> true 'Non empty string tests' str != '' ==> true str !== '' ==> true str.length != 0 ==> true str.length > 0 ==> true !!str ==> true (str) ? true : false ==> true 'Compare two empty strings' (em1 == em2) ==> true (em1 === em2) ==> true prompt$ jsish -u emptyString.jsi [PASS] emptyString.jsi
Julia
<lang Julia> blank = "" nonblank = "!"
println("The length of blank is ", length(blank)) println("That blank is empty is ", isempty(blank)) println("That blank is not empty is ", !isempty(blank))
println() println("The length of nonblank is ", length(nonblank)) println("That nonblank is empty is ", isempty(nonblank)) println("That nonblank is not empty is ", !isempty(nonblank)) </lang>
- Output:
The length of blank is 0 That blank is empty is true That blank is not empty is false The length of nonblank is 1 That nonblank is empty is false That nonblank is not empty is true
K
<lang K> variable: ""
0=#variable
1
0<#variable
0</lang>
Kotlin
<lang scala>fun main(args: Array<String>) {
val s = "" println(s.isEmpty()) // true println(s.isNotEmpty()) // false println(s.length) // 0 println(s.none()) // true println(s.any()) // false
}</lang>
LabVIEW
This image is a VI Snippet, an executable image of LabVIEW code. The LabVIEW version is shown on the top-right hand corner. You can download it, then drag-and-drop it onto the LabVIEW block diagram from a file browser, and it will appear as runnable, editable code.
Lambdatalk
In Lambdatalk primitives working on sequences of words begin with "S." <lang scheme> '{def emptyString } -> emptyString
'{S.empty? {emptyString}} -> true
'{S.empty? hello} -> false
'{= {S.length {emptyString}} 0} -> true </lang>
langur
You can use empty quote marks or the ZLS token. <lang langur>val .zls = ZLS writeln .zls == "" writeln .zls != "" writeln len(.zls)</lang>
- Output:
true false 0
Lasso
<lang Lasso>//Demonstrate how to assign an empty string to a variable. local(str = string) local(str = )
//Demonstrate how to check that a string is empty.
- str->size == 0 // true
not #str->size // true
//Demonstrate how to check that a string is not empty. local(str = 'Hello, World!')
- str->size > 0 // true
- str->size // true</lang>
Latitude
Assigning the empty string. <lang latitude>s := "". s := String clone.</lang>
Checking whether a string is empty. <lang latitude>s == "". s empty?. s length == 0.</lang>
Note that all strings are truthy in Latitude, so simply checking the truthiness of a string is an insufficient means to check whether it is empty.
LFE
<lang lisp> > (set str "") () > (length str) 0 > (=:= 0 (length str)) true > (=:= 0 (length "apple")) false > (=:= "apple" "") false > (=/= "apple" "") true > (=:= str "") true > (=:= "apple" '()) false > (=/= "apple" '()) true > (=:= str '()) true > (case str ('() 'empty) ((cons head tail) 'not-empty)) empty > (case "apple" ('() 'empty) ((cons head tail) 'not-empty)) not-empty </lang>
Lhogho
Lhogho is a Logo compiler for Windows and Linux <lang logo>make "str " ;make null-string word print empty? :str ;prints 'true' print not empty? :str ;prints 'false' </lang>
Liberty BASIC
<lang lb> 'assign empty string to variable a$ = "" 'check for empty string if a$="" then print "Empty string." if len(a$)=0 then print "Empty string." 'check for non-empty string if a$<>"" then print "Not empty." if len(a$)>0 then print "Not empty." </lang>
Lingo
<lang lingo>str = EMPTY -- same as: str = "" put str=EMPTY -- 1 put str<>EMPTY -- 0</lang>
LOLCODE
The empty string is a false value in LOLCODE, and is thus amenable to use as the condition of an O RLY? <lang LOLCODE>HAI 1.3
I HAS A string ITZ "" string, O RLY?
YA RLY, VISIBLE "STRING HAZ CONTENZ" NO WAI, VISIBLE "Y U NO HAS CHARZ?!"
OIC
KTHXBYE</lang>
Lua
<lang Lua> -- create an empty string 3 different ways str = "" str = str = [[]]
-- test for empty string if str == "" then
print "The string is empty"
end
-- test for nonempty string if str ~= "" then
print "The string is not empty"
end
-- several different ways to check the string's length if string.len(str) == 0 then
print "The library function says the string is empty."
end if str:len() == 0 then
print "The method call says the string is empty."
end if #str == 0 then
print "The unary operator says the string is empty."
end
</lang>
M2000 Interpreter
Easy reply for this task <lang M2000 Interpreter> A$="" Print A$<>"", A$="", Len(A$)=0 </lang>
Depends of variable visibility, and what we want to do: To make a new local, to shadow a local or a global on.
<lang M2000 Interpreter> Module Checkit {
\\
\\ Part 1: Make global variable, alter it, make a shadow local or global one, use temporary variable
\\
Global a$="ok"
Module Global What {
Print a$
}
Module Checkit {
Print a$="ok"
a$<=""
Print a$=""
a$<="ok2"
a$=""
Print a$="", a$<>""
Global a$="ok again"
Module Inner {
Print a$="ok again"
}
Inner
What \\ now What use new global a$
\\ display list of public variables
List
\\ we can define locals using Def, but raise error if local exist
Try {
Def a$="error"
}
Def b$
Print b$=""
For This {
\\ block for temporary definitions
For i=1 to 10 {
Local a$=str$(i)
}
\\ we get 10 more a$
List
Print a$=" 10"
}
Print a$=""
List
\\ using current stack
}
\\ we call always a local module, or a global, but not this module,
\\ no recursion for standard call for modules.
\\ we have to use Call Checkit to call this module recursive
Checkit
What \\ now what use old global a$
Print a$<>"" ' true
List
\\
\\ Part 2: Pass an empty string to a variable through stack of values
\\
Module Checkit2 {
\\ read make a local by default
Read a$
Print a$="" ' true
For This {
Push "Hello"
Read New a$
Print a$="Hello"
List
}
Print a$=""
}
Checkit2 ""
Print a$<>"" ' true
Module Checkit3 {
\\ using Set we change to global space, for the end of line
Set Read a$
Print a$="" ' true
list
}
Checkit3 ""
Print a$<>"" ' true
Module Checkit4 {
\\ this make a local if no global exist
\\ so if global exist, alter the global one
Let a$=Letter$
Print a$="" ' true
list
}
Checkit4 ""
Print a$="" ' true
} Checkit </lang>
Maple
<lang Maple> s := ""; # Create an empty string evalb(s = ""); # test if the string is empty evalb(s <> ""); # test if the string is not empty </lang>
Mathematica / Wolfram Language
<lang Mathematica> str=""; (*Create*) str==="" (*test empty*) str=!="" (*test not empty*) </lang>
MATLAB / Octave
<lang Matlab> % Demonstrate how to assign an empty string to a variable.
str = ; % Demonstrate how to check that a string is empty. isempty(str) (length(str)==0) % Demonstrate how to check that a string is not empty. ~isempty(str) (length(str)>0)</lang>
Maxima
<lang maxima>s: ""$
/* check using string contents */ sequal(s, ""); not sequal(s, "");
/* check using string length */ slength(s) = ""; slength(s) # "";</lang>
Mercury
There's nothing special about empty strings in Mercury.
<lang Mercury>S = "", % assignment
( if S = "" then ... else ... ), % checking if a string is empty
( if not S = "" then ... else ... ), % checking if a string is not empty</lang>
min
The bool operator returns false on an empty string and true on a non-empty string. We can define empty? as the negation of bool.
<lang min>(bool not) :empty?
"" empty? puts!
"Rosetta Code" empty? puts!</lang>
- Output:
true false
Mirah
<lang mirah>empty_string1 = "" empty_string2 = String.new
puts "empty string is empty" if empty_string1.isEmpty() puts "empty string has no length" if empty_string2.length() == 0 puts "empty string is not nil" unless empty_string1 == nil</lang>
Nanoquery
<lang nanoquery>s = ""
if len(s)=0
println "s is empty"
else
println "s is not empty"
end</lang>
Nemerle
Assign an empty string: <lang Nemerle>def empty = ""; mutable fill_later = "";</lang> Check if a string is empty/not empty: <lang Nemerle>a_string == ""; a_string != 0; a_string.Length == 0; a_string.Length > 0;</lang>
NESL
<lang nesl>my_empty_string = "";
% To make sure it is empty, we can ask whether its length is equal to zero. %
- my_empty_string == 0;</lang>
- Output:
my_empty_string = "" : [char] it = T : bool
NetRexx
<lang NetRexx>/* NetRexx */ options replace format comments java crossref symbols binary
s1 = -- assignment s2 = "" -- equivalent to s1 parse '.' . s3 . -- parsing a token that doesn't exist results in an empty string
strings = [s1, s2, s3, ' ']
loop s_ = 0 to strings.length - 1
say (Rexx s_).right(3)':\-' select when strings[s_] == then say ' "'strings[s_]'" is really empty' when strings[s_].length = 0 then say ' "'strings[s_]'" is empty' when strings[s_] = then say ' "'strings[s_]'" looks empty but may not be' when strings[s_].length > 0 then say ' "'strings[s_]'" is not empty' otherwise nop end end s_
return </lang>
- Output:
0: "" is really empty 1: "" is really empty 2: "" is really empty 3: " " looks empty but may not be
Nim
<lang nim>var x = ""
if x == "":
echo "empty"
if x != "":
echo "not empty"
- Alternatively:
if x.len == 0:
echo "empty"
if x.len > 0:
echo "not empty"</lang>
NS-HUBASIC
<lang NS-HUBASIC>10 S$="" 20 IF S$<>"" THEN O$="NOT " 30 PRINT "THE STRING IS "O$"EMPTY."</lang>
Nyquist
Lisp Syntax
<lang lisp> (setf emptystring "") ;binds variable'emptystring' to the empty string ""
(let ((emptystring "")) ;; Binds local variable 'emptystring' to the empty string ""
(when (string-equal emptystring "") ;;case insensitive string comparison (print "Is an empty string")) ;;bad argument error if not a string (when (stringp emptystring) (print "Is a string")) (when (not (stringp emptystring)) (print "Is not a string")) (when (and (stringp emptystring)(= (length emptystring) 0)) (print "Is an empty string")) (when (and (stringp emptystring)(> (length emptystring) 0)) (print "Is a non-empty string")))
</lang>
SAL Syntax
<lang sal> define variable emptystring = "" ;binds variable'emptystring' to the empty string ""
if emptystring = "" then
print "is empty string"
else
print "is not empty string"
</lang>
Audacity plug-in (LISP syntax)
<lang lisp>
- nyquist plug-in
- version 4
- type tool
- name "Empty string"
(setq emptystring "") ;; Define global variable
(if (string= emptystring "") ;;case sensitive string comparison
"The string is empty." "The string is not empty.")
</lang>
Audacity plug-in (SAL syntax)
<lang Nyquist>
- nyquist plug-in
- version 4
- codetype sal
- type tool
- name "Empty string"
define variable emptystring = "a" ;; Define global variable
- The ternary operator is #?
return #?(emptystring = "",
"The string is empty.",
"The string is not empty.")
</lang>
oberon-2
<lang oberon2> MODULE EmptyString; IMPORT Out; VAR
str: ARRAY 64 OF CHAR;
BEGIN
str := "";
Out.String("for str := ");Out.Char('"');Out.Char('"');Out.Char(';');Out.Ln;
Out.String("checking str = ");Out.Char('"');Out.Char('"');Out.String(" Is Empty? ");Out.Bool(str = "");Out.Ln;
Out.String("checking str[0] = 0X. Is Empty? ");Out.Bool(str[0] = 0X);Out.Ln;
str := "Hello Rossetta";
Out.String("for str :=");Out.Char('"');Out.String(str);Out.Char('"');Out.Char(";");Out.Ln;
Out.String("checking str = ");Out.Char('"');Out.String(str);Out.Char('"');Out.String(" Is Empty? ");Out.Bool(str = "");Out.Ln;
Out.String("checking str[0] = 0X. Is Empty? ");Out.Bool(str[0] = 0X);Out.Ln;
END EmptyString. </lang>
- Output:
for str := ""; checking str = "" Is Empty? TRUE checking str[0] = 0X. Is Empty? TRUE for str :="Hello Rossetta"; checking str = "Hello Rossetta" Is Empty? FALSE checking str[0] = 0X. Is Empty? FALSE
Objeck
<lang objeck> s := ""; if(s->IsEmpty()) {
"s is empty"->PrintLine();
} else{
"s is not empty"->PrintLine();
}; </lang>
OCaml
<lang ocaml>let is_string_empty s =
(s = "")
let () =
let s1 = "" and s2 = "not empty" in Printf.printf "s1 empty? %B\n" (is_string_empty s1); Printf.printf "s2 empty? %B\n" (is_string_empty s2);
- </lang>
- Output:
s1 empty? true s2 empty? false
Oforth
isEmpty can be used on all collections, not only strings.
<lang Oforth>"" isEmpty "" isEmpty not</lang>
Ol
<lang ol>
- define the empty string
(define empty-string "")
- three simplest tests for 'the-string emptiness
(if (or
(string-eq? the-string "")
(string=? the-string "")
(eq? (string-length the-string) 0))
(print "the-string is empty")
- four simplest tests for 'the-string not emptiness
(if (or
(not (string-eq? the-string ""))
(not (string=? the-string ""))
(not (eq? (string-length the-string) 0))
(less? 0 (string-length the-string)))
(print "the-string is NOT empty))
</lang>
ooRexx
should work with each and every REXX interpreter/compiler. <lang oorexx>v= w=' ' if v== Then Say 'v contains the empty string'< If length(w)>0 Then Say 'Variable w does not contain the empty string' If w= Then Say 'this is not a good test' </lang>
- Output:
v contains the empty string Variable w does not contain the empty string this is not a good test
OpenEdge/Progress
Strings can be stored in CHARACTER and LONGCHAR variables. Both are initially empty. Both can also be unknown. A CHARACTER has a maximum length of approx 32000 bytes.
<lang progress>DEFINE VARIABLE cc AS CHARACTER.
IF cc > THEN
MESSAGE 'not empty' VIEW-AS ALERT-BOX.
ELSE IF cc = ? THEN
MESSAGE 'unknown' VIEW-AS ALERT-BOX.
ELSE /* IF cc = */
MESSAGE 'empty' VIEW-AS ALERT-BOX.
</lang>
PARI/GP
<lang parigp>a=""; isEmpty(s)=s=="" \\ Alternately: isEmpty(s)=#s==0 isNonempty(s)=s!="" \\ Alternatively: isNonempty(s)=#s</lang>
Pascal
See Delphi or Free Pascal
Perl
<lang perl>if ($s eq "") { # Test for empty string
print "The string is empty";
} if ($s ne "") { # Test for non empty string
print "The string is not empty";
}</lang>
In Perl, an empty string is often used to represent a false value. <lang Perl>$s = ""; if ($s) { ... } # false
- to tell if a string is false because it's empty, or it's plain not there (undefined)
$s = undef; if (defined $s) { ... } # false; would be true on ""
- though, perl implicitly converts between strings and numbers, so this is also false
$s = "0"; if ($s) { ... } # false; also false on "000", "0.0", "\x0", "0 with text", etc
- but a string that converts to number 0 is not always false, though:
$s = "0 but true"; if ($s) { ... } # it's true! black magic!</lang>
Phix
<lang euphoria>string s
s = "" -- assign an empty string
if length(s)=0 then -- string is empty if s="" then -- string is empty
if length(s)!=0 then -- string is not empty if s!="" then -- string is not empty</lang>
PHP
<lang Php><?php
$str = ; // assign an empty string to a variable
// check that a string is empty if (empty($str)) { ... }
// check that a string is not empty if (! empty($str)) { ... }
// we could also use the following if ($str == ) { ... } if ($str != ) { ... }
if (strlen($str) == 0) { ... } if (strlen($str) != 0) { ... }</lang>
PicoLisp
The empty string is represented by 'NIL' in PicoLisp. During input, two subsequent double quotes '""' return the symbol NIL. <lang PicoLisp># To assign a variable an empty string: (off String) (setq String "") (setq String NIL)
- To check for an empty string:
(or String ..) (ifn String ..) (unless String ..)
- or a non-empty string:
(and String ..) (if String ..) (when String ..)</lang>
PL/I
<lang PL/I>Dcl s Char(10) Varying; s = ; /* assign an empty string to a variable. */ if length(s) = 0 then ... /* To test whether a string is empty */ if length(s) > 0 then ... /* to test for a non-empty string */ </lang>
PowerShell
Assignment (the type identifier is optional): <lang PowerShell> [string]$alpha = "abcdefghijklmnopqrstuvwxyz" [string]$empty = ""
- or...
[string]$empty = [String]::Empty </lang> Tests: <lang PowerShell> [String]::IsNullOrEmpty($alpha) [String]::IsNullOrEmpty($empty) </lang>
- Output:
False True
Prolog
<lang prolog>assign_empty_string(Variable) :- Variable = "".
is_empty_string(String) :- String == "". not_empty_string(String) :- String \== "". </lang>
PureBasic
In PureBasic we can just test a string for truth to determine if it has a value. <lang PureBasic>Procedure.s isStringEmpty(a.s)
If a ProcedureReturn "String is not empty, it contains '" + a + "'." Else ProcedureReturn "String is empty, or null." EndIf
EndProcedure
If OpenConsole()
Define a.s = "" Define b.s = "stuff" PrintN(isStringEmpty(a)) PrintN(isStringEmpty(b)) Print(#CRLF$ + #CRLF$ + "Press ENTER to exit"): Input() CloseConsole()
EndIf</lang>
- Output:
String is empty, or null. String is not empty, it contains 'stuff'.
Python
The empty string is printed by Python REPL as '', and is treated as boolean false (as are most empty container types, by convention). Any non-empty string, including '0', is always treated as True in a boolean context.
<lang python>s =
if not s or s == :
print("String is empty")
if len(s) == 0:
print("String is empty")
else:
print("String not empty")
- boolean test function for python2 and python3
- test for regular (non-unicode) strings
- unicode strings
- None
def emptystring(s):
if isinstance(s, (.__class__ , u.__class__) ):
if len(s) == 0:
return True
else
return False
elif s is None:
return True
</lang>
Quite BASIC
<lang Quite BASIC>10 let s="" 20 if s="" then let o="" 30 if s<>"" then let o="not " 40 print "The string is ";o;"empty."</lang>
R
<lang R>s <-
if (s == ) cat('Empty\n')
- or
if (nchar(s) == 0) cat('Empty\n')
if (s != ) cat('Not empty\n')
- or
if (nchar(s) > 0) cat('Not empty\n')</lang>
Racket
<lang Racket>#lang racket
(define empty-string "") (define (string-null? s) (string=? "" s)) (define (string-not-null? s) (string<? "" s))</lang>
Raku
(formerly Perl 6)
<lang perl6>my $s = ; say 'String is empty' unless $s; say 'String is not empty' if $s;</lang>
Unlike in Perl 5, only empty strings test as false - the string "0" tests as true now.
Rascal
<lang rascal>str s = ""; if (s=="") print("string s is empty"); if (s!="") print("string s is not empty"); </lang> Or the build-in operator: <lang rascal>import String; if (isEmpty(s)) print("string s is empty"); if (isEmpty(s)) print("string s is not empty");</lang>
Red
<lang Red>Red [] s: copy "" ;; assign empty string ?? s if empty? s [print "string is empty "] ;; check if string is empty s: "abc" prin s unless empty? s [print " not empty"] </lang>
- Output:
s: "" string is empty abc not empty >>
Retro
Create an empty string and assign it to a variable. In these keepString is used to ensure that the string is permanent. <lang Retro> ( by creating a variable ) "" keepString variable: foo
( by setting an existing variable 'foo' ) "" keepString !foo </lang>
Checking that a string is empty. A string with a length of zero is assumed to be empty.
<lang Retro>
- emtpy? ( $-f ) getLength 0 = ;
"" empty? putn "hello" empty? putn </lang>
Check that a string is not empty.
<lang Retro>
- notEmpty? ( $-f ) getLength 0 > ;
"" notEmpty? putn "hello" notEmpty? putn </lang>
REXX
<lang rexx>/*REXX program shows how to assign an empty string, & then check for empty/not-empty str*/
/*─────────────── 3 simple ways to assign an empty string to a variable.*/
auk= /*uses two single quotes (also called apostrophes); easier to peruse. */ ide="" /*uses two quotes, sometimes called a double quote. */ doe= /*··· nothing at all (which in this case, a null value is assigned. */
/*─────────────── assigning multiple null values to vars, 2 methods are:*/
parse var doe emu pug yak nit moa owl pas jay koi ern ewe fae gar hob
/*where emu, pug, yak, ··· (and the rest) are all set to a null value.*/
/*───or─── (with less clutter ─── or more, depending on your perception)*/
parse value 0 with . ant ape ant imp fly tui paa elo dab cub bat ayu
/*where the value of zero is skipped, and the rest are set to null,*/
/*which is the next value AFTER the 0 (zero): nothing (or a null).*/
/*─────────────── how to check that a string is empty, several methods: */
if cat== then say "the feline is not here." if pig=="" then say 'no ham today.' if length(gnu)==0 then say "the wildebeest's stomach is empty and hungry." if length(ips)=0 then say "checking with == instead of = is faster" if length(hub)<1 then method = "this is rather obtuse, don't do as I do ···"
nit= /*assign an empty string to a lice egg.*/ if cow==nit then say 'the cow has no milk today.'
/*─────────────── how to check that a string isn't empty, several ways: */
if dog\== then say "the dogs are out!"
/*most REXXes support the ¬ character. */
if fox¬== then say "and the fox is in the henhouse." if length(rat)>0 then say "the rat is singing" /*an obscure-ish (or ugly) way to test.*/
if elk== then nop; else say "long way obtuse for an elk to be tested."
if length(eel)\==0 then fish=eel /*a fast compare (than below), & quick.*/ if length(cod)\=0 then fish=cod /*a not-as-fast compare. */
/*────────────────────────── anyway, as they say: "choose your poison." */</lang>
Ring
<lang ring> cStr = NULL # empty string if cStr = NULL
see "cstr is an empty string!" + nl
else
see "cstr is not empty string!" + nl
ok </lang>
Robotic
<lang robotic> set "$string" to "" if "$string.length" = 0 then "empty"
- "Not an empty string."
end
- "empty"
- "Empty string"
end </lang>
Ruby
Create an empty string <lang ruby>s = "" s = String.new s = "any string"; s.clear</lang>
These expressions all evaluate to true to determine emptiness: <lang ruby>s == "" s.eql?("") s.empty? s.length == 0 s[/\A\z/]
- also silly things like
s.each_char.to_a.empty?</lang>
Non-empty expressions, in addition to simply negating the above expressions: <lang ruby>s != "" s.length > 0 s[/./m]</lang>
Note that we can not do the following, because the empty string is equivalent to true in Ruby (Boolean values#Ruby): <lang ruby>if s then puts "not empty" end # This code is wrong!</lang>
Run BASIC
<lang runbasic>var$ = "" ' -------------- 'empty string ' ------------- if var$="" then print "String is Empty" if len(var$)=0 then print "String is Empty" ' ------------- 'not empty string ' ------------- if var$<>"" then print "String Not empty." if len(var$)>0 then print "String Not empty."</lang>
Rust
<lang rust>let s = ""; println!("is empty: {}", s.is_empty()); let t = "x"; println!("is empty: {}", t.is_empty()); let a = String::new(); println!("is empty: {}", a.is_empty()); let b = "x".to_string(); println!("is empty: {}", b.is_empty()); println!("is not empty: {}", !b.is_empty());</lang>
Scala
<lang scala>// assign empty string to a variable val s="" // check that string is empty s.isEmpty // true s=="" // true s.size==0 // true // check that string is not empty s.nonEmpty // false s!="" // false s.size>0 // false</lang>
Scheme
<lang scheme>(define empty-string "") (define (string-null? s) (string=? "" s)) (define (string-not-null? s) (string<? "" s))</lang>
Seed7
<lang seed7># assign empty string to a variable s := ""
- check that string is empty
s = ""
- check that string is not empty
s <> ""</lang>
Self
<lang self> "Put an empty string in a slot called 'str'" str: .
"Check that string is empty" str isEmpty.
"Check that string is not empty" str isEmpty not.</lang>
SenseTalk
<lang self> set emptyString to ""
put emptyString
put emptyString is empty
put emptyString is not empty </lang>
- Output:
True False
Sidef
Create an empty string: <lang ruby>var s = ""; var s = String.new;</lang>
These expressions all evaluate to true to determine emptiness: <lang ruby>s == ""; s.length == 0; s.is_empty; s ~~ /^\z/; s ~~ /\A\z/;</lang>
Non-empty expressions, in addition to simply negating the above expressions: <lang ruby>s != ""; s.length > 0; s ~~ /./s; s !~ /^\z/;</lang>
Smalltalk
<lang smalltalk> "Assign empty string to a variable" str := .
"Check that string is empty" str isEmpty.
"Check that string is not empty" str isEmpty not. </lang>
SNOBOL4
An assignment statement with nothing to the right of the = operator assigns the empty string (or, as it is more commonly called in SNOBOL, the null string). <lang snobol4>* ASSIGN THE NULL STRING TO X
X =
- CHECK THAT X IS INDEED NULL
EQ(X, NULL) :S(YES)
OUTPUT = 'NOT NULL' :(END)
YES OUTPUT = 'NULL' END </lang>
- Output:
NULL
Standard ML
<lang sml>(* Assign empty string to a variable *) val s = "" (* Check that a string is empty*) s = "" (* Check that a string is nonempty *) s <> ""</lang>
Stata
<lang stata>scalar s=""
display s==""
- Alternatively, check the length
display length(s)==0</lang>
Swift
<lang swift>var s = "" if s.isEmpty { // alternately, s == ""
println("s is empty")
} else {
println("s is not empty")
}</lang>
Tcl
The only special position that the empty string has in Tcl is that a great many commands return it, and the REPL of tclsh and wish doesn't print it. Otherwise, it is just like any other value. <lang tcl>set s "" if {$s eq ""} {puts "s contains an empty string"} if {$s ne ""} {puts "s contains a non-empty string"}</lang> There are other ways to check for emptiness and non-emptiness too (though the above are favored for reasons of simplicity, clarity and speed): <lang tcl>if {[string equal $s ""]} {puts "is empty"} if {[string length $s] == 0} {puts "is empty"} if {[string compare $s ""] != 0} {puts "is non-empty"}</lang>
TorqueScript
Assign an empty string to $empty
$empty = "";
Check if $empty is an empty string
if($empty $= "") { echo("$empty is an empty string."); }
Check if $empty is not an empty string
if($empty !$= "") { echo("$empty is not an empty string."); }
TUSCRIPT
<lang tuscript> $$ MODE TUSCRIPT s="" IF (s=="") PRINT "s is an empty string" IF (s!="") PRINT "s is a non-empty string" </lang>
- Output:
s is an empty string
TXR
Pattern Matching
<lang txr>@(bind a "")</lang>
If a is unbound, a binding is created, containing the empty string.
If a is already bound, bind succeeds if a contains the empty string, and the pattern matching continues at the next directive.
Or else a failure occurs, triggering backtracking behavior.
TXR Lisp
<lang txrlisp>(defvarl a "")
(if (equal a "")
(format t "empty string\n"))
(set a "nonempty")
(if (zerop (length a))
(format t "guess what?\n"))</lang>
UNIX Shell
<lang bash># assign an empty string to a variable s=""
- the "test" command can determine truth by examining the string itself
if [ "$s" ]; then echo "not empty"; else echo "empty"; fi
- compare the string to the empty string
if [ "$s" = "" ]; then echo "s is the empty string"; fi if [ "$s" != "" ]; then echo "s is not empty"; fi
- examine the length of the string
if [ -z "$s" ]; then echo "the string has length zero: it is empty"; fi if [ -n "$s" ]; then echo "the string has length non-zero: it is not empty"; fi</lang>
When using comparison operators, it is crucial to double-quote the variable within the conditional expression. This will ensure the shell sees the correct number of arguments. For example, if one were to write [ $s = "" ], then after variable substitition, the shell will try to evaluate [ = "" ] which is a syntax error.
Ursa
<lang ursa>decl string s set s ""
if (= s "") out "empty" endl console else out "not empty" endl console end if</lang>
VAX Assembly
<lang VAX Assembly>desc: .ascid "not empty" ;descriptor (len+addr) and text .entry empty, ^m<>
tstw desc ;check length field
beql is_empty
;... not empty
clrw desc ;set length to zero -> empty
is_empty:
;... empty
ret
.end empty</lang>
VBA
<lang vb> dim s as string
' assign an empty string to a variable (six bytes): s = "" ' assign null string pointer to a variable (zero bytes, according to RubberduckVBA): s = vbNullString ' if your VBA code interacts with non-VBA code, this difference may become significant!
' test if a string is empty: if s = "" then Debug.Print "empty!" ' or: if Len(s) = 0 then Debug.Print "still empty!"
'test if a string is not empty: if s <> "" then Debug.Print "not an empty string" 'or: if Len(s) > 0 then Debug.Print "not empty." </lang>
VBScript
See VBA
Visual Basic
See VBA
Visual Basic .NET
Compiler: Roslyn Visual Basic (language version >= 14, e.g. with Visual Studio 2015)
In brief
<lang vbnet>Dim s As String
' Assign empty string: s = "" ' or s = String.Empty
' Check for empty string only (false if s is null): If s IsNot Nothing AndAlso s.Length = 0 Then End If
' Check for null or empty (more idiomatic in .NET): If String.IsNullOrEmpty(s) Then End If</lang>
In depth
Note: implementation information provided in comments was obtained reflecting .NET libraries and viewing the .NET Core reference source and may not be correct or remain relevant as time passes.
In .NET Core, functions defined in Microsoft.VisualBasic are only available for .NET Core 3.0 and above.
<lang vbnet>Option Strict On
Module Program
Sub Main()
' Equality is somewhat convoluted in .NET, and VB doesn't help by adding legacy means of comparison.
' The methods above are the author's recommendation for each case.
' Some also return true if the string is Nothing/null; this is noted in the description for those that
' do.
' s is initialized to Nothing. It is a variable of the System.String type that is a null reference and is not
' the empty string.
Dim s As String = Nothing
' Alias Console.WriteLine(Boolean) with a shorter name to make the demonstration code less verbose.
Dim P As Action(Of Boolean) = AddressOf Console.WriteLine
' Assign the empty string literal to s.
s = ""
Assign String.Empty to s.
s = String.Empty
' The empty string literal is the same object reference as String.Empty because of string interning, meaning the
' behavior of the two is identical.
' From this point on, "" will be used instead of String.Empty for brevity.
'#Is operator
' The Is operator tests for reference equality. However, which strings are interned is a CLR implementation
' detail and may be unreliable when comparing non-empty strings. The equivalent in C# would be (object)s == "".
' Note that there is no such operator as Object.op_Equality(Object, Object): the use of the == operator for
' types of type Object is a C# language feature.
P(s Is "")
'#Object.ReferenceEquals(Object, Object)
' The previous line is semantically to the following, though it does not involve a method call.
P(Object.ReferenceEquals(s, ""))
'#= Operator
'True for Nothing.
' The VB.NET compiler does not use the System.String implementation of the equality operator. Instead, it emits
' a call to a method in the Visual Basic runtime, Operators.CompareString, which checks for reference equality
' before calling System.String.CompareOrdinal(String, String), which checks again for reference equality before
' comparing character-by-character.
P(s = "")
'#Microsoft.VisualBasic.CompilerServices.Operators.CompareString(String, String, Boolean)
'True for Nothing.
' Equivalent to the above line, though methods in the CompilerServices namespace are not meant for use by
' regular code.
' The third argument indicates whether to use a textual comparison (e.g. ignore case and diacritics).
P(0 = CompilerServices.Operators.CompareString(s, "", False))
'#Microsoft.VisualBasic.Strings.StrComp(String, String, [CompareMethod])
'True for Nothing.
' A wrapper around CompareString that is intended for use.
P(0 = StrComp(s, ""))
'#String.op_Equality(String, String)
' It is possible to directly call the equality operator of System.String, which is implemented as a call to
' String.Equals(String).
P(String.op_Equality(s, ""))
'#String.Equals(String, String)
' Call the static method defined on the String type.
' first calls Object.ReferenceEquals and then, after verifying that both are strings of the same length,
' compares the strings character-by-character.
P(String.Equals(s, ""))
'#Object.Equals(Object, Object)
' First checks for reference equality and whether one or both of the arguments is Nothing. It then invokes the
' instance Equals method of the left parameter.
P(Object.Equals(s, ""))
'#String.Equals(String)
' The method is called with the string literal as the receiver because a NullReferenceException is thrown if s
' is Nothing.
P("".Equals(s))
'#Microsoft.VisualBasic.Strings.Len(String)
'True for Nothing.
' Check the length using Microsoft.VisualBasic.Strings.Len(String). This method returns s?.Length (see below).
P(0 = Len(s))
'#String.Length
' Check the Length property. The ?. (null-conditional) operator is used to avoid NullReferenceException. The Equals
' call above can also be done this way.
' A method call must be added because the equality operator propagates Nothing/null (that is, the result of the
' expression is Nullable(Of Boolean)). This has the side effect of making it behave "correctly" for null.
P((s?.Length = 0).GetValueOrDefault())
' The If statement automatically unwraps nullable Booleans, however.
If s?.Length = 0 Then
End If
'#String.Length
' A more traditional version of the null-conditional using a guard clause.
' Both the null-conditional and this are noticeably (~4 times) faster than "".Equals(s). In general, it appears that
' for empty strings, using the length is faster than using an equality comparison.
P(s IsNot Nothing AndAlso s.Length = 0)
'#String.IsNullOrEmpty(String)
'True for Nothing
' A static method of System.String that returns true if the string is Nothing or its length is zero.
P(String.IsNullOrEmpty(s))
'#System.Collections.Generic.EqualityComparer(Of String).Default.Equals(String, String)
' The EqualityComparer(Of T) class provides default implementations when an IEqualityComparer(Of T) is required.
' The implementation for String calls String.Equals(String).
P(EqualityComparer(Of String).Default.Equals(s, ""))
Console.WriteLine()
' Each of the methods described above, except testing for a non-empty string.
P(s IsNot "")
P(Not Object.ReferenceEquals(s, ""))
P(s <> "")
P(0 <> CompilerServices.Operators.CompareString(s, "", False))
P(0 <> StrComp(s, ""))
P(String.op_Inequality(s, ""))
P(Not String.Equals(s, ""))
P(Not Object.Equals(s, ""))
P(Not "".Equals(s))
P(Len(s) <> 0)
P((s?.Length <> 0).GetValueOrDefault())
P(s Is Nothing OrElse s.Length <> 0)
P(Not String.IsNullOrEmpty(s))
P(Not EqualityComparer(Of String).Default.Equals(s, ""))
End Sub
End Module</lang>
- Output:
True True True True True True True True True True True True True True False False False False False False False False False False False False False False
Wee Basic
<lang Wee Basic>let string$="" if string$="" print 1 "The string is empty." elseif string$<>"" print 1 "The string is not empty." endif end</lang>
Wren
<lang ecmascript>var isEmpty = Fn.new { |s| s == "" }
var s = "" var t = "0" System.print("'s' is empty? %(isEmpty.call(s))") System.print("'t' is empty? %(isEmpty.call(t))")</lang>
- Output:
's' is empty? true 't' is empty? false
XLISP
STRING-NULL? returns true if its argument is a string of length zero. In a REPL:
<lang scheme>[1] (define my-empty-string "") ;; assign an empty string to a variable
MY-EMPTY-STRING [2] (string-null? my-empty-string)
- T
[3] (string-null? "A non-empty string")
()</lang>
XPL0
<lang XPL0>code Text=12; string 0; \use zero-terminated convention, instead of MSb set char S; [S:= ""; \assign an empty string if S(0) = 0 then Text(0, "empty "); S:= "Hello"; if S(0) # 0 then Text(0, "not empty "); ]</lang>
zkl
<lang zkl>s:=""; // or s:=String, String is the object "" s.toBool() //-->False if (s) println("not empty")</lang>
Zoomscript
For typing: <lang Zoomscript>var string string = "" if eq string "" print "The string is empty." else print "The string is not empty." endif</lang> For importing:
¶0¶var string¶0¶string = ""¶0¶if eq string ""¶1¶print "The string is empty."¶0¶else¶1¶print "The string is not empty."¶0¶endif
ZX Spectrum Basic
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