runtime library and global namespace

Does th开发者_如何学Ce runtime library pollute the global namespace?

I don't think you really understand the terms you are using, but the names in the C++ Standard Library exist in the std namespace, so the answer is no. The names in the header files that originated in the C Standard Library are placed in the global namespace, if you #include them via the .h filenames, such as:

#include <stdio.h>

if you #include them like this:

#include <cstdio>

then the names exist in both global and std namespaces.

The reason for placing objects in the std namespace is not so much to avoid "namespace polution", which is hardly a value neutral term, but to avoid name clashes.

The runtime library is required to use reserved identifiers. Without namespace qualification, these must begin with two underscores: __start, etc.

You are not allowed to use reserved names. The library is not allowed to use your names. If either crosses over to the other, it is "pollution" which is illegal.

Essentially, the situation is the same for C and C++ except, as the other answers point out, in C++ most standard library names have namespace qualification.

Most of the library cleanly goes in namespace std: -- however, for backwards compatibility with C, you may choose to "pollute" the global namespace by including old headers like <math.h> (which puts lots of names in the global namespace) instead of the proper new ones like <cmath> (which uses the std: namespace properly).