Les fonctions et en-têtes C doivent-ils être utilisés à partir de l'espace de noms `std::` ou de l'espace de noms global en C ?

Using C Headers in C++: Namespaces or Global Scope?

In C++, one can access C functions and headers by modifying the header file names (e.g., stdio.h to cstdio, stdlib.h to cstdlib). However, it raises the question of whether to use functions from the std:: namespace or the global namespace for these headers in C++ code.

Namespace vs. Global Scope in C++

According to the C++11 Standard, every C header with a ".h" extension behaves as if its names are placed within both the global namespace and the namespace std. It remains unspecified whether these names are first declared in the std:: namespace and injected into the global namespace or vice versa.

Preferred Approach

To ensure compatibility with future C++ revisions and remove potential ambiguities, it is recommended to use the "cname" headers and declare and define functions within the std:: namespace. Using the old ".h" headers is deprecated and has been identified for removal in upcoming revisions.

Example Code

Prefer the following code snippet:

#include <cstdio>

int main() {
    std::printf("Hello world\n");
}

over:

#include <stdio.h>

int main() {
    printf("Hello world\n");
}

Conclusion

While it's possible to use both std:: and the global namespace for C functions and headers in C++, the preferred approach is to include the "cname" headers and use the declarations and definitions from the std:: namespace for consistency with future C++ revisions and to avoid potential issues.

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