extern "c" usage?!!

[Medvedev]

What's that preprocessor do
#ifdef __cplusplus
extern "C" {
#endif
..
..
..
#ifdef __cplusplus
}
#endif

and how you say extern "C" , i mean how u extern constant!!

 

[Medvedev]

extern "C"
{

}

.. causes any functions inside the braces to have
"C linkage", so that they can be called from C
functions. There's nothing about 'constant' here.

sorry , but what differ C++ functions from C ones

 

[Jim Langston]

sorry , but what differ C++ functions from C ones

C++ functions have overloading. C functions do not. This means there is
only one definition for a C function, there can be more than one for a C++
function. Compilers typcially handle this by "mangling". This will change
the name of the C++ function in the object file so the linker can
differentiate between calling parameters.

stating:
extern "C" {
tells the compiler not to mangle the function names, there will only be one
declaration for each function, so then when it is linked it has C linkage,
the function name would be the same as if it was a C function, and C
programs/objects can call the function as they can now link to them.

 

[James Kanze]

sorry , but what differ C++ functions from C ones

Whatever the implementation wants. There's no fundamental
reason for two different languages to use the same calling
conventions. One typical difference might be that in C++, the
call stack is cleaned up in the called function (since it
involves calling destructors, etc.), where as in C, it is
cleaned up in the callee (since historically, C didn't have
prototypes, and allowed calling a function with extra arguments,
which were ignored). Also, C++ has overloading, which means
that some sort of information concerning the type and number of
arguments must be maintained in the object file. And because C
allowed extra arguments, a C compiler will not want to do this.