Re: extern "C"

James Kanze <>
Fri, 5 Sep 2008 03:02:07 -0700 (PDT)
On Sep 5, 4:52 am, "northern_RATT" <> wrote:

<snip>> I need to be able to mix C and C++.

The main program is written in C and needs to access C++
code. To be more specific it's a user defined function in
fluent, but this should not be relevant.

I've allready read that i need to use the extern "C"
construction but i don't seem to be doing it right.


OK. Pardon a rank amature who only lurks here, BUT....
This looks like backwards logic to me. I thought that
'extern C' is a way for C++ code to call undecorated C code(?)

No. 'extern "C"' tells the compiler to use C linkage, period.
A C++ function can be declared 'extern "C"', in which case, it
uses C linkage (but is C++ in every other way), and can be
called from a C program.

The classical example is the function passed to things like
pthread_create (Unix) or CreateThread (Windows); since this
function is called from C code, it must be 'extern "C"'.

Not the otherway around!
Not that I have ever needed to face this, but I thought that C
calling C++ code needs some type of wrapper?

And how would you implement the wrapper? If you can't call C++
from C, you can't implement it in C, and if you implement it in
C++, you couldn't call it from C.

Typically, C++ code does require a wrapper, because it is using
argument types which C can't handle; the wrapper takes care of
any necessary type conversions. But thw wrapper itself is also

James Kanze (GABI Software)
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