Empty string: Difference between revisions

Content added Content deleted

Inline

Revision as of 14:54, 24 March 2017

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.

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:=

ACL2

To check if a string is empty: <lang Lisp>(= (length str) 0)</lang>

ALGOL 68

Works with: ALGOL 68G version Any - tested with release 2.8.win32

<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>

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>

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>

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.

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>/* 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 */ if (strlen(str) == 0) { ... } /* or compare to a known empty string, same thing. "== 0" means strings are equal */ if (strcmp(str, "") == 0) { ... } </lang>

C++

<lang cpp>#include <string>

// ...

std::string str; // a string object for an empty string

if (str.empty()) { ... } // to test if string is empty

// we could also use the following if (str.length() == 0) { ... } if (str == "") { ... }</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>

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

      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>

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>

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>

Elena

<lang elena>#import extensions.

program = [

   var s := emptyLiteralValue.

   if (s is &empty)
       [ console writeLine:"'": s :"' is empty". ].
                       
   if (s is &nonempty)
       [ console writeLine:"'": s :"' is not empty". ].

].</lang>

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

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.

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>

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>

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>

I

<lang i>software { var s = ""

if len(s) = 0 print("Empty string!") end

if s != "" 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>

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

Translation of: J

<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.

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>

LFE

Translation of: Clojure

Translation of: Common Lisp

Translation of: Erlang

<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>str = "" -- create empty string

-- 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</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>

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>

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>

oberon-2

Works with: oo2c version 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>

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>

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

PARI/GP

<lang parigp>a=""; isEmpty(s)=s=="" \\ Alternately: isEmpty(s)=#s==0 isNonempty(s)=s!="" \\ Alternatively: isNonempty(s)=#s</lang>

Pascal

See Delphi

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>

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.

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

Works with: SWI-Prolog version 7

<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:

   print('String s is empty.')

if s:

   print('String s is not 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>

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>

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.

emtpy? ( $-f ) getLength 0 = ;

"" empty? putn "hello" empty? putn </lang>

Check that a string is not empty.

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>

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>

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>

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

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>

VBA

<lang vb> dim s as string

' assign an empty string to a variable: s = ""

' 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>

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>