tobi303 tobi303 - 25 days ago 6x
C++ Question

Which header should I include for `size_t`?

According to

is defined in several headers, namely


And, since C++11, also in


First of all I wonder why this is the case. Isn't this in contradiction to the DRY principle? However, my question is:

Which one of the above headers should I include to use
? Does it matter at all?


Assuming I wanted to minimize the functions and types I was importing I'd go with cstddef as it doesn't declare any functions and only declares 6 types. The others focus on particular domains (strings, time, IO) that may not matter to you.

Note that csttddef only guarantees to define std::size_t, that is, defining size_t in namespace std, although it may provide this name also in the global namespace (effectively, plain size_t).

In contrast, stddef.h (which is also a header available in C) guarantees to define size_t in the global namespace, and may also provide std::size_t.