extern "C" doubt

[jaden5165]

 extern "C" {
		char *getwd(char *);
	};         

May I know what does this code means? As I know when there is any C header then we should use extern "C" if we want to compile them into a c++ module.Am i right?
But what is char *getwd(char *); since it is not a header of C. I need explicit explanation and simple example.Thanks.

[MiiNiPaa]

There is no difference between that and:

//header.h
char *getwd(char *);

//Main.cpp
 extern "C" {
#include "header.h"
}; 

Because #include directive just copy-pasting all content of header into target file.
Some info on extern "C":
http://stackoverflow.com/questions/1041866/in-c-source-what-is-the-effect-of-extern-c
http://www.cplusplus.com/forum/general/1143/

[jaden5165]

extern "C" {
		char *getwd(char *);
	};

DOes the above code doin anythg?Since char * doesnt state where the path of current directory save to.The code above actually done ntg or is doing thing as you mentioned in the previous post ? How i know char *getwd(char *); is written in header.h ?

[keskiverto]

1. char *getwd(char *); is a declaration of a function that takes a char pointer, returns a char pointer, and has name 'getwd'. Where did you find that piece of code?

man getwd wrote:

For portability and security reasons, use of getwd() is deprecated.

2. The extern "C" tells the linker and the C++ compiler that this declared function prototype corresponds to an implementation of the function that has been compiled with C compiler.

3. When you use functions and types written by someone else and available as libraries, you also use the documentation of those libraries to find out what they have and do.

[MiiNiPaa]

It is telling linker that that fuction is using C-style calls, name mangling etc. So you can link file containing that function which was compiled by C-compiler.

Basically it tells: this function was compiled in C, not C++. It is special, threat it accordingly during code generation.

[JLBorges]

> Basically it tells: this function was compiled in C, not C++.

It tells: This function has C linkage (name binding, parameter passing and return).

#include <iostream>
#include <functional>
#include <initializer_list>
 
extern "C" void foo( std::initializer_list<int> init_lst, std::function< void(int) > fn )
{ for( const auto& i : init_lst ) fn(i) ; }
 
int main()
{
    foo( { 0, 1, 2, 3, 4 }, [] ( int i ) { std::cout << i << ' ' ; } ) ;
}

http://ideone.com/kISTPX