Platform independent size_t Format specifiers in c?

Question

I want to print out a variable of type size_t in C but it appears that size_t is aliased to different variable types on different architectures. For example, on one machine (64-bit) the following code does not throw any warnings:

size_t size = 1;
printf("the size is %ld", size);

but on my other machine (32-bit) the above code produces the following warning message:

warning: format '%ld' expects type 'long int *', but argument 3 has type 'size_t *'

I suspect this is due to the difference in pointer size, so that on my 64-bit machine size_t is aliased to a long int ("%ld"), whereas on my 32-bit machine size_t is aliased to another type.

Is there a format specifier specifically for size_t?

Answer 1

Yes: use the z length modifier:

size_t size = sizeof(char);
printf("the size is %zu
", size);  // decimal size_t ("u" for unsigned)
printf("the size is %zx
", size);  // hex size_t

The other length modifiers that are available are hh (for char), h (for short), l (for long), ll (for long long), j (for intmax_t), t (for ptrdiff_t), and L (for long double). See §7.19.6.1 (7) of the C99 standard.