Question

It seems on XCode I need to use std::size_t instead of just size_t on Visual C++. But this is a pain as I don’t really want to have to #include <cstddef> and change every size_t to std::size_t in my code… in my Windows code size_t just works without including any additional files.

Is there a way to make my existing code work in XCode, (maybe through the .pch file?) or are GCC/MSVC++ fundamentally different in this regard and my code needs to use std::size_t in order to be cross-platform?

Answer 1

According to the C++03 standard, 17.4.1.2.4:

Except as noted in clauses 18 through 27, the contents of each header cname shall be the same as that of the corresponding header name.h, as specified in ISO/IEC 9899:1990 Programming Languages C (Clause 7), or ISO/IEC:1990 Programming Languages—C AMENDMENT 1: C Integrity, (Clause 7), as appropriate, as if by inclusion. In the C++ Standard Library, however, the declarations and definitions (except for names which are defined as macros in C) are within namespace scope (3.3.5) of the namespace std.

In other words, by choosing to use <cstddef> instead of <stddef.h>, you’re specifically asking for the type size_t to be within the namespace std.

So, here are the choices:

1. Use <stddef.h> instead, so size_t is in the top-level namespace, as suggested by Jesse Good.

2. Use <cstddef> and use std::size_t.

3. Use <cstddef> and use a using declaration to pull size_t into the top-level namespace, as suggested by cnicutar.

Of course you could rely on the fact that one particular version of one compiler/library/platform lets you get away with it, or write different code for each platform, or wrap the whole thing up with autoconf, or write a code generator or sed-based preprocessor, or whatever… but why?