How static library in c++ work with name mangle?

Question

I ask this for understanding, In c there is no name mangling but c++ has. How this works for example say I have following files

• exlib.hpp header file
• exlib.cpp function implemented file
• exapp.cpp main function using exlib

File exlib.hpp

#ifndef EXLIB
#define EXLIB

#include <iostream>

int sum(int, int);
int sum(int, int, int);
int sum(int, int, int, int);

#endif

File exlib.cpp

#include "exlib.hpp"

int sum(int a, int b)
{
    std::cout << "In sum(int, int)" << std::endl;
    return a + b;
}

int sum(int a, int b, int c)
{
    std::cout << "In sum(int, int, int)" << std::endl;
    return a + b + c;
}

int sum(int a, int b, int c, int d)
{
    std::cout << "In sum(int, int, int, int)" << std::endl;
    return a + b + c + d;
}

File exapp.cpp

#include "iostream"
#include "exlib.hpp"

int main()
{
    std::cout << "Sum = " << sum(1, 1) << std::endl;
    std::cout << "Sum = " << sum(2, 2, 2) << std::endl;
    std::cout << "Sum = " << sum(3, 3, 3, 3) << std::endl;
}

Compile

$ g++ -c exlib.cpp
$ g++ exapp.cpp exlib.o -o exapp
$ ./exapp

sum in exlib.o are name mangled right ?

output:

Sum = In sum(int, int)
2
Sum = In sum(int, int, int)
6
Sum = In sum(int, int, int, int)
12

1. How sum correctly called after name mangle in main ?, There is any rules for name mangling that same name is replaced in main or How they identify?
2. All programming language mangle name in same way ?

Thanks.

Answer 1

While C++ offers Polymorphism (i.e. different things can be named equal in the same scope by using other features for distinguishing them), this is not supported by linkers (neither in statical nor dynamical linking). So, C++ compilers uses name mangling. (The other features are used to decorate the original identifier to produce a unique name.)

A C++ compiler compiles each C++ file (aka. translation unit) on its own. Hence, it is obvious that the name mangling has to be done in a unique, reproducible way by this compiler. I.e. the same declaration has to be mapped to the same symbol always. Otherwise, it would be impossible for the linker to resolve symbols that were declared (only) in one file and defined in another.

However, there isn't a general name-mangling standard (e.g. as part of the C++ standard).

So, even on the same platform, the binary codes produced by two different compilers may be incompatible due to different name-mangling (as well as other details). (For MS Visual C++, this makes even binaries from distinct versions incompatible.)

To overcome this, there exist Application Binary Interfaces (ABIs) for certain platforms (e.g. Linux). One detail of an ABI is a standardized name-mangling.