Complie and link C++ code in C

[Micko]

Hello people,
it's been a long since last time I worked with C and C++. Is it possible to link Cpp code in C?
What I mean is this:
In basics, it comes to this...

I have two files:
Test_cpp.h

int test_cpp(int);

Test_cpp.cpp

int test_cpp(int x)
{
    return x+2;
}

and main.c /*in other C project in which Test_cpp.h and Test_cpp.cpp are included*/

#include <stdio.h>
#include "Test_CPP.h"

int main(int argc, char *argv[])
{
  printf("&#37;d", test_cpp(4));
  return 0;
}

Is it possible to use extern keyword to make this work?

Thanks

[l2u]

Of course.. Shouldnt be a problem..

[Dave_Sinkula]

http://www.parashift.com/c++-faq-lit...c-and-cpp.html

[Micko]

Hmm, I'm still having problems:
I'm using Dev-Cpp in which I have created C project with the following files:

Header Test_Cpp.h:

#ifndef  TEST_CPP_H
#define TEST_CPP_H
extern "C" int test_cpp(int);
#endif

Implementation file Test_Cpp.cpp:

#include "Test_Cpp.h"
int test_cpp(int x)
{
    return x+2;
}

Main.c:

#include <stdio.h>
#include "Test_Cpp.h"

int main()
{
  printf("&#37;d", test_cpp(4));
  return 0;
}

I'm getting this error on second line:
3 C:\Dev-Cpp\C_Cpp_Dev\Test_Cpp.h syntax error before string constant

What is the possible reason for this? It's like compiler doesn't recognize extern keyword...

P.S. Test_Cpp.cpp is already compiled with C++ compiler.

[tabstop]

A C compiler doesn't know what "extern "C"" means. If you want C++ code to be called from a C program, you have to compile Test_Cpp.cpp with

extern "C" int test_cpp(int x)

so that the C++ compiler knows to mangle the name differently for export. But your C header file would just have the normal prototype.

[Dave_Sinkula]

http://www.parashift.com/c++-faq-lit....html#faq-32.1

You must use your C++ compiler when compiling main() (e.g., for static initialization)

[vart]

32.4 is more interesting i think

[brewbuck]

A C compiler doesn't know what "extern "C"" means. If you want C++ code to be called from a C program, you have to compile Test_Cpp.cpp with

extern "C" int test_cpp(int x)

so that the C++ compiler knows to mangle the name differently for export. But your C header file would just have the normal prototype.

But that causes the function to be a true-blue C function, meaning overloading doesn't work any more. You can't just go around in a C++ library declaring things extern "C". You have to write a small wrapper, in C++, which transfers control from C to C++. The wrapper is declared extern "C" so the C code can call it, but because it is a C++ function, it is able to call other C++ functions.

In this case, instead of making test_cpp(int x) an extern "C", I'd write a wrapper function:

/* In some header common to the C and C++ code... */
extern "C" int test_cpp_C(int x);
/* In Test_Cpp.cpp */
int test_cpp_C(int x)
{
    // Make sure exceptions can't get up into the C code
    try
    {
        return test_cpp(x);
    }
    catch(...) {}
}

Now the C code calls test_cpp_C() and that function transfers control to the C++ function. If test_cpp() is overloaded, you need to write a wrapper for each one.

If the C++ throws an exception, you have to communicate that to the C code in a way it can understand, but that's a whole other problem.

[jian2587]

question:
if I want to call C code from C++, apart from adding extern declarations in the C++ code, what else do I do? I gather it's this.
1. Compile C code with C compiler, creates object code A.
2. Compile C++ code with C++ compiler, creates object code B.
3. Use C++ linker to link A and B. <-- how do I do this?
Is this correct?

[matsp]

question:
if I want to call C code from C++, apart from adding extern declarations in the C++ code, what else do I do? I gather it's this.
1. Compile C code with C compiler, creates object code A.
2. Compile C++ code with C++ compiler, creates object code B.
3. Use C++ linker to link A and B. <-- how do I do this?
Is this correct?

As a concept, that's what you do.

As to how you do step 3, usually it's simple, just . E.g. in gcc/g++ you do:

$ gcc -c -Wall A.c -o A.o
$ g++ -c -Wall B.cpp -o B.o
$ g++ A.o B.o -o myapp

Other compilers obvious call themeselves different things, and use slightly different flagnames, but otherwise the principle is the same.

You can of course merge step 2 & 3 in this case by doing:

$ g++ A.o -Wall B.cpp -o myapp

--
Mats