How to avoid namespace collision in C and C++

Question

I can use using namespace directive to avoid identifier/variable name collision, but what happens when file names or library names collision happens in large projects.

In C the conventional approach is to add files recursively using #include_next directive. How can I achieve the same in C++ without using the #include_next directive and address the issue of duplicate file names among applications and shared libraries. An example, a work around the class() function in AIX math.h clashing with identifiers named "class".

/* GNU Lesser GPLv2.1 or later */
#ifndef FFMPEG_COMPAT_AIX_MATH_H
#define FFMPEG_COMPAT_AIX_MATH_H

#define class some_text

#include_next <math.h>

#undef class

#endif /* FFMPEG_COMPAT_AIX_MATH_H */

EDIT: Can I use, for example class machine-instruction-set where the binary has to run on multiple platforms? Can there be namespace collision in such case?

Answer 1

I can use using namespace directive to avoid identifier/variable name collision

Quite to the contrary, using namespace directive introduces collisions. You resolve collisions by specifying scopes, e.g. std::vector<> vs. boost::numeric::ublas::vector<>.

... but what happens when file names or library names collision happens in large projects?

Filename collisions are easy to prevent by being systematic: organize your headers so that they mimic your namespaces, e.g. boost::numeric::ublas::vector<> comes from #include <boost/numeric/ublas/vector.hpp>. And don't pile headers and sources of different libraries in one directory, so that you can include headers with the same name using a different directory prefix, e.g. #include <lzma/version.h> vs. #include <linux/version.h>.