Where do I find the definition of size_t, and what is it used for?

Question

I see variables defined with this type but I don't know where it comes from, nor what is its purpose. Why not use int or unsigned int? (What about other "similar" types? Void_t, etc).

Answer 1

From Wikipedia

The stdlib.h and stddef.h header files define a datatype called size_t1 which is used to represent the size of an object. Library functions that take sizes expect them to be of type size_t, and the sizeof operator evaluates to size_t.

The actual type of size_t is platform-dependent; a common mistake is to assume size_t is the same as unsigned int, which can lead to programming errors,2 particularly as 64-bit architectures become more prevalent.

From C99 7.17.1/2

The following types and macros are defined in the standard header stddef.h

<snip>

size_t

which is the unsigned integer type of the result of the sizeof operator