Question

Consider this little program:

#include <stdio.h>
int main()
{
    char c = 0xFF;
    printf("%d\n", c);

    return 0;
}

Its output is -1, as expected (considering char is signed in my
system). What I’m trying to do is to make it print 255. This is of
course a simplification of the real situation, where I can’t just define
c as unsigned.

The first possible change would be using %u as formatter instead, but
the usual type promotion rules apply here, and the number is printed as
2³² – 1.

So is there any way to read the signed char as unsigned before it gets
promoted to an int? I could create a pointer to a unsigned char set to the
address of c, and dereference it later, but not sure if this is the best
approach.

Answer 1

c is being promoted using signed promotion rules. Cast c to unsigned to use unsigned promotion.

printf("%u\n", (unsigned char)c);

Unsigned char will be promoted to unsigned int.