unable to link between c and c++

[jeevs]

I have a class whose member I need to access in c prog.
I have defined the class object as extern.

when I tried to access the class member in c it says undefine reference.

where as I'm able to access the same class members in different places.
please help me

[Banfa]

You will not be able to access any class members from C because a class is a C++ construct that C is unaware of.

What you can do is declare functions with C naming convention in a C++ file

Header
[code=cpp]
#ifdef __cplusplus
extern "C" {
#endif

extern void MyFunction(void );

#ifdef __cplusplus
}
#endif
[/code]
cpp code
[code=cpp]
#include "header"

void MyFunction(void )
{
// Code here that accesses the class
}
[/code]

c code
[code=c]
#include "header"

void SomeFunction(vo id)
{
MyFunction();
}
[/code]
This enables C code to call into C++ modules, you then put the C++ code (code accessing classes for instance) inside the function with the C naming convention.

[weaknessforcats]

Continuing Banfa's reply, you can write a function (extern "C") in C++ that calls the member function of the class and then you can call this function from C.

These are called buck-passer functions and are quite common.