type

size_t

<cstdio>
Unsigned integral type
Alias of one of the fundamental unsigned integer types.

It is a type able to represent the size of any object in bytes: size_t is the type returned by the sizeof operator and is widely used in the standard library to represent sizes and counts.

In <cstdio>, it is used as the type of some parameters in the functions fread, fwrite and setvbuf, and in the case of fread and fwrite also as its returning type.

C++