Question

In the following obj-c function, what does the %qx format specifier mean (I would imaging the question also holds for use with printf and co.)

+(NSString*)stringForHash:(uint64_t)hash
{
    return [NSString stringWithFormat:@"%qx", hash];
}

My guess is that it means print the 64 bits in hex, as opposed to %x which would only print 32 bits. I cannot however find a good reference confirming this anywhere. What does q stand for? Can it be used in conjunction anything else than x in format specifiers?

Answer 1

From Wikipedia:

it is a pre-C99 extension meaning

“q – For integer types, causes printf to expect a 64-bit (quad word) integer argument. Commonly found in BSD platforms”