Empty string: Difference between revisions
(→{{header|D}}: added D) |
m (Not sure what that was there for...) |
||
Line 51: | Line 51: | ||
System.out.println("s is not empty"); |
System.out.println("s is not empty"); |
||
}</lang> |
}</lang> |
||
--[[User:Fwend|Fwend]] 22:51, 4 July 2011 (UTC) |
|||
=={{header|Perl 6}}== |
=={{header|Perl 6}}== |
Revision as of 23:11, 4 July 2011
Some languages have syntax or semantics for dealing specifically with empty strings.
The task is to:
- 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.
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 empty. <lang d>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'); assert(isEmpty(s1)); assert(isEmptyNotNull(s2));
}
bool isEmpty(string s) {
return !s.length;
}
bool isEmptyNotNull(string s) {
return s is "";
}</lang>
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>
Perl 6
In Perl 6 we can't just test a string for truth to determine if it has a value. The string "0" will test as false even though it has a value. Instead we must test for length.
<lang perl6>my $s = ; say 'String is empty' unless $s.chars; say 'String is not empty' if $s.chars;</lang>
Python
<lang python>s = if not s:
print('String s is empty.')
if s:
print('String s is not empty.')</lang>