Question

an ancient code I maintain originally had this:

NSUInteger readUnicode(NSMutableString *string, signed char const * buf, signed long int offset, size_t bufsize)
{   
    NSUInteger initLength = [string length];
    signed char const * start = buf + offset;
    NSLog (@"--------> start: %S", start);

    [string appendFormat:@"%S", start];
    return [string length] - initLength;
}

with XCode throwing a warning “Format specifies type ‘const unsigned short *’ but the argument has type ‘const signed char *’ and suggesting to change appendFormat:@”%S” to appendFormat:@”%s”

when I did change %S to %s I started getting only ONE character in return string, regardless of the input.

So instead I changed the code to:

NSUInteger readUnicode(NSMutableString *string, signed char const * buf, signed long int offset, size_t bufsize)
{
    NSUInteger initLength = [string length];

    const unsigned short * start = (const unsigned short * )buf + offset;
    NSLog (@"--------> start: %S", start);

    [string appendFormat:@"%S", start];
    return [string length] - initLength;
}

… and now I seem to be getting all the characters and without the warning.
Is this the way to deal with the warning ? Or perhaps I could/should have done something else ? (Other than changing the type of the input buf)

Thank you.

Answer 1

Is this the way to deal with the warning ?

Perhaps not exactly. If you work with wide strings, why don’t you declare your function to do so?

NSUInteger readUnicode(NSMutableString *string, unichar const *buf, signed long int offset, size_t bufsize)
                                                ^^^^^^^
                                       Note the use of "unichar"!

Then you don’t need the ugly cast, you won’t get the warning and your program wouldn’t invoke undefined behavior.