Is size_t the word size?

Question

Is size_t the word size of the machine that compiled the code?

Parsing with g++, my compiler views size_t as an long unsigned int

Answer 1

size_t was, orignally, just a typedef in sys/types.h (traditionally on Unix/Linux). It was assumed to be 'big enough' for, say, the maximum size of a file, or the maximum allocation with malloc. However, over time, standard committees grabbed it, and so it wound up copied into many different header files, protected each time with its own #ifdef protection from multiple definition. On the other hand, the emergence of 64-bit systems with very big potential file sizes clouded its role. So it's a bit of a palimpset.

Language standards now call it out as living in stddef.h. It has no necessary relationship to the hardware word size, and no compiler magic. See other answers with respect to what those standards say about how big it is.