c++ - Best Practise and Semantics of namespace nested functions and the use of extern "C" -

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i creating c++ library c-abi interface.

this how gcc treats extern "c" qualifier regards mangling:

namespace x {      extern "c" int monkey(int x) {         return 1;     }      int chimpanzee(int x) {         return 1;     } }

the relevant nm output:

00000000004005cd t _zn1x10chimpanzeeei 00000000004005bf t monkey

question: want leave functions involved in c-abi inside namespace, maximum flexibility reuse. important note: once library has been compiled give linker map file (gcc) or module definition file (msvc).

  1. is mangling output standard behaviour -- other major compilers (msvc in specific) strip mangling ?
  2. are pitfalls or best-practises regarding placing functions in name-space when involved in external abi?
  3. will interfere c-abi export of de-mangled functions during link time ?

this msvc.

the namespace not name-mangled, name of namespace incorporated in function's (or object's) name when name mangling occurs. process undocumented, described here.

answering specific questions jumping around:

1) there no standard-defined behavior regarding name mangling. standard says implementations provides c-compatible linkage extern "c" constructs:

7.5.3 [linkage specifications]

every implementation shall provide linkage functions written in c programming language, "c", , linkage c + + functions, "c++". [example:

complex sqrt(complex); // c + + linkage default  extern "c" { double sqrt(double); // c linkage }

—end example]

ultimately means since c has no concept of namespaces, if extern "c" functions or objects in namespaces, exported names lose namespace qualification. leads to...

3) yes, can have linkage problem. try this:

main.h

#ifndef main_api #   define main_api __declspec(dllexport) #endif  namespace x {     extern "c" main_api void foo(); };  namespace y {     extern "c" main_api void foo(); };

main.cpp

#include <cstdlib> #include <iostream> using namespace std; #define main_api __declspec(dllexport) #include "main.h"  void x::foo() {     cout << "x::foo()\n"; }  void y::foo() {     cout << "y::foo()\n"; }  int main() { }

this emit linker error because extern "c"-ed versions of x::foo() , y::foo() have lost namespace identification, end same name: foo()

2) best practices regarding this. if must export c-abi functions in namespaces, have careful names end exporting not same. degree, defeats purpose of using namespace in first place. can this:

#ifndef main_api #   define main_api __declspec(dllexport) #endif  namespace x {     extern "c" main_api void x_foo(); };  namespace y {     extern "c" main_api void y_foo(); };

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