accessing C function from C++

nuliknol · 07-05-2010, 10:26 AM

Hi,

i have an open source application that was developed in C++ (it uses objects and namespaces all over the place). I also have another application that was developed in C. Now i am trying to insert the code made in C into C++ application, but when i do that , i get this error on compilation of the source code:

Code:

error: 'mpi_init_vars' was not declared in this scope

the function mpi_init_vars() is not part of object oriented programming and it doesn't belong to any scope, it was compiled into an object file and i am linking it with all objects of C++ application.

How can invoke the C function from C++ object oriented code?

Thanks in advance.

ForzaItalia2006 · 07-05-2010, 10:53 AM

Quote:

Originally Posted by nuliknol

i have an open source application that was developed in C++ (it uses objects and namespaces all over the place). I also have another application that was developed in C. Now i am trying to insert the code made in C into C++ application, but when i do that , i get this error on compilation of the source code:

Code:

error: 'mpi_init_vars' was not declared in this scope

the function mpi_init_vars() is not part of object oriented programming and it doesn't belong to any scope, it was compiled into an object file and i am linking it with all objects of C++ application.

How can invoke the C function from C++ object oriented code?

C++ mangles function names, thought mpi_init_vars() will become _Zmpi_init_vars (or similar). Please check out the extern "C" {} functionality in your favourite WEB search.

Andi

paulsm4 · 07-05-2010, 11:01 AM

Hi, nuliknol -

1. C++ (unlike "classic C") does NOT allow "implicit declarations". You MUST declare function "mpi_init_vars()" before you use it.

2. As ForzaItalia2006 said, you must also use "externC {}" syntax when you declare it.

3. The declaration should usually be in a header file. If you're using somebody else's library, you should already have a .h header. Otherwise, you can easily write your own:

Example header ("mympi.h"; change as appropriate):

Code:

#ifndef MY_MPI_H
#define MY_MPI_H

#ifdef __cplusplus
extern "C" {
#endif
void mpi_init_vars ();
#ifdef __cplusplus
}
#endif 

#endif
/* MY_MPI_H *

It looks ugly. Heck - it IS ugly

But it should get you going!

'Hope that helps .. PSM