Platform independent size_t Format specifiers in c?
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?
& somewhere?
warning: format '%ld' expects type 'long int *', but argument 3 has type 'size_t *' when it probably should be saying warning: format '%ld' expects type 'long int', but argument 3 has type 'size_t'. Were you maybe using scanf() instead when you got these warnings?
Yes: use the z length modifier:
size_t size = sizeof(char);
printf("the size is %zu\n", size); // decimal size_t ("u" for unsigned)
printf("the size is %zx\n", 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.
Yes, there is. It is %zu (as specified in ANSI C99).
size_t size = 1;
printf("the size is %zu", size);
Note that size_t is unsigned, thus %ld is double wrong: wrong length modifier and wrong format conversion specifier. In case you wonder, %zd is for ssize_t (which is signed).
MSDN, says that Visual Studio supports the "I" prefix for code portable on 32 and 64 bit platforms.
size_t size = 10;
printf("size is %Iu", size);
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size_tand anssize_t; the latter is seldomly used.%zu, because the argument is unsigned.zlength modifier is not part of C89/C90. If you're aiming for C89-compliant code, the best you can do is cast tounsigned longand use thellength modifier instead, e.g.printf("the size is %lu\n", (unsigned long)size);; supporting both C89 and systems withsize_tlarger thanlongis trickier and would require using a number of preprocessor macros.