Name Mangling in C++


In  C++ we can write multiple functions of  same name with different parameter type is call function overloading. To achieve function overloading c++ uses a concept know as "name mangling".

For differentiating the function name c++ compiler change the function name by adding information about arguments

Ex:
actual function prototype:   void show(int arg)
After name mangling:         void show_i(int arg)

actual function prototype:   void show(float arg)
After name mangling:         void show_f(float arg)

Here the function show(int) & show(float) changes to show_i(int) & show_f(float)

Actually in developer think that he/she is calling show function but compiler changer that show to show_i or show_f according to the arguments.

C doesn't support "name mangling"; so we can't call c function in c++ project.
To call c function in c++ "extern" key word is used.

How do we call C function from C++

Ans: Suppose we have 2 files main.cpp & add.c

                 C File
------------------add.c-----------------------                                                                         
    void f(int i)
    {
      printf("I am in f=%d",i);
    }

    int g(double d)
    {
      printf("I am in g=%lf",d);
    }
--------------------------------------------------------
         C++ File                 
----------------------main.cpp-----------------------

    extern "C" void f(int); // one way                 

    extern "C" {    // another way
            int g(double);
            double h();
     };

    void code(int i, double d)
    {
            f(i);
            int ii = g(d);
            // ...
    }
-----------------------------------------------

We can include header files in this way as well

    extern "C" {
      // Get declaration for f(int i, char c, float x)
      #include "my-C-code.h"
    }


How do we call C++ function from C

Ans: Calling function f & g from c code

                   C File
-----------------------main.c-----------------------                                                                        

    void code(int i, double d)
    {
            f(i);
            int ii = g(d);
            // ...
    }
-----------------------------------------
              C++ File                 
----------------------add.cpp-----------------------

    extern "C" void f(int); // one way                 

    extern "C" {    // another way
            int g(double);
            double h();
     };

    void f(int i)
    {
      printf("I am in f=%d",i);
    }

    int g(double d)
    {
      printf("I am in g=%lf",d);
    }

----------------------------------------------

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