about extern c

[sekhar_ps]

can any one tell me whats the use of extern c with an example

[Banfa]

extern "C" defines a function in a C++ file with C function naming instead of the name mangling that C++ applies (in order to enable overloading). That means that the function can be called from a C module as well as a C++ module

// Header.h
 
#ifdef __cplusplus
extern "C" {
#endif
 
void printHelloWorld(void); 
 
#ifdef __cplusplus
}
#endif
 
// cplusplus.cpp
 
#include <iostream>
#include "header.h"
 
using namespace std;
 
void printHelloWorld(void)
{
    cout << "Hello World !" << endl;
}
 
// c.c
 
#include "header.h"
 
int main(int argc, char *argv[])
{
    printHelloWorld();
}