How to use NULL character with NSString?

Question

In PHP, I can call base64_encode(\"\\x00\". $username. \"\\x00\". $password) and the \"\\x00\" represents a NULL character.

Now, in Objecti

Answer 1

Your syntax is correct. NSString just doesn't handle NULL bytes well. I can't find any documentation about it, but NSString will silently ignore %c format specifiers with an argument of 0 (and on that note, the character constant '\0' expands to the integer 0; that is correct). It can, however, handle \0 directly embedded into an NSString literal.

See this code:

#import 
int main (int argc, char const *argv[])
{
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    NSString *stringByChars = [NSString stringWithFormat:@"-%c%c%c%c-",0,0,0,0];
    NSString *stringByEscapes = [NSString stringWithFormat:@"-\0\0\0\0-"];
    NSLog(@"  stringByChars: \"%@\"", stringByChars);
    NSLog(@"            len: %d", [stringByChars length]);
    NSLog(@"           data: %@", [stringByChars dataUsingEncoding:NSUTF8StringEncoding]);
    NSLog(@"stringByEscapes: \"%@\"", stringByEscapes);
    NSLog(@"            len: %d", [stringByEscapes length]);
    NSLog(@"           data: %@", [stringByEscapes dataUsingEncoding:NSUTF8StringEncoding]);
    [pool drain];
    return 0;
}

returns:

  stringByChars: "--"
            len: 2
           data: <2d2d>
stringByEscapes: "-
            len: 6
           data: <2d000000 002d>

(Note that since the stringByEscapes actually contains the NULL bytes, it terminates the NSLog string early).