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cprintfc89size-tc-libraries

Is the %zu specifier required for printf?

We are using C89 on an embedded platform. I attempted to print out a size_t, but it did not work: 

#include <stdio.h>
int main(void) {
    size_t n = 123;
    printf("%zu\n",n);
    return 0;
}

Instead of 123, I got zu.
Other specifiers work correctly.

If size_t exists shouldn't zu also be available in printf?
Is this something I should contact my library vendor about, or is a library implementation allowed to exclude it?

Solution

  • If size_t exists shouldn't zu also be available in printf?

    size_t existed at least since C89 but the respective format specifier %zu (specifically the length modifier z) was added to the standard only since C99.

    So, if you can't use C99 (or C11) and had to print size_t in C89, you just have to fallback to other existing types, such as:

    printf("%lu\n", (unsigned long)n);