linking C++ functions in a C program

[abasili]

Hi everyone, I'm trying to compile a C++ function and then call it from
a C program.
Since Google is my friend I've ended up to this link which seems very clear:

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

Unfortunately it does not work.
Here is what I'm doing:

-----------------------------------------
//main.c

#include "mylib.h"

int main (int argc, char *argv[]){
foo();
return 0;
}
-----------------------------------------
//mylib.h

#indef __cplusplus
extern "C"{
#endif

void foo();

#ifdef __cplusplus
}
#endif
-----------------------------------------
//mylib.cc

#include <iostream>
#include "mylib.h"

using namespace std; // don't know what for!

void foo(){
cout<<"Hello World!\n";
}
-----------------------------------------
Thanks a lot for any suggestion.

Al

[Ian Collins]

abasili wrote:

Hi everyone, I'm trying to compile a C++ function and then call it from
a C program.
Since Google is my friend I've ended up to this link which seems very
clear:

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

Unfortunately it does not work.

It does if you follow all the points. The first two are often overlooked.

Here is what I'm doing:

-----------------------------------------
//main.c

#include "mylib.h"

int main (int argc, char *argv[]){
foo();
return 0;
}

How are you building your executable?

--
Ian Collins

[abasili]

Ian Collins wrote:

>
It does if you follow all the points. The first two are often overlooked.

Here is my Makefile

>
How are you building your executable?

Here is my Makefile
-----------------------------------------

OS = OS_LINUX
CC = gcc
CXX = g++
AR = ar

INCMYLIB = mylib.h

INC = $(INCMYLIB)

OBJMYLIB = mylib.o

OBJ = $(OBJMYLIB)

ROOTINCL = $(ROOTSYS)/include

MYLIB = mylib.a

CFLAGS = -g -D$(OS) -Wall -O2 -fno-strict-aliasing \
-I/usr/X11R6/include/ -I/usr/X11R6/include/X11
-I$(ROOTINCL) \

BOOLFLAG = -D_BOOL
ROOTFLAG = `root-config --libs`
CCFLAG = $(BOOLFLAG) $(ROOTFLAG)

LDFLAGS = -L/usr/X11R6/lib -z muldefs
LOADMYLIBES = $(MYLIB) -lm -lX11 -Xlinker -Bstatic -lforms -Xlinker
-Bdynamic

INT = main

EXT =

EXE = $(EXT) $(INT)
#------------------------------------------------------------------------------

all: $(OBJ) $(MYLIB) $(EXE)

#------------------------------------------------------------------------------

%.o: %.c $(INC)
$(CC) -c -o $*.o $*.c $(CFLAGS)

%.o: %.cc $(INC)
$(CXX) -c -o $*.o $*.cc $(CFLAGS) $(BOOLFLAG)

$(MYLIB): $(OBJ)
$(AR) cru $(MYLIB) $(OBJ)

%: %.c $(MYLIB)
$(CC) -o $* $*.c $(CFLAGS) $(LDFLAGS) $(LOADMYLIBES)

%: %.cc $(MYLIB)
$(CXX) -o $* $*.cc $(CFLAGS) $(CCFLAG) $(LDFLAGS) $(LOADMYLIBES)

#------------------------------------------------------------------------------
export:
cp -p -f $(EXT) /usr/local/bin

#------------------------------------------------------------------------------

clean:
rm -f *~ *.bak *.o $(EXE) core

#============== =============== =============== =============== =============== ====
This Makefile is used to compile several programs and be able to use
somebody else library, here I reduced it to the minimum only to study
this case.
Thanks,

Al

[abasili]

Ian Collins wrote:

It does if you follow all the points. The first two are often overlooked.

I'm sorry about that, actually compiling with g++ the main works.
The main problem is that my C program cannot be compiled with g++, there
are too many incompatibiliti es and a lot of work has been already done in C.
So I have to find another way to call a C++ function through my C code.

[abasili]

abasili wrote:

So I have to find another way to call a C++ function through my C code.

Problem is solved.
I created a new main.cc which will call my main_C.c which will be
compiled with gcc, while the main.cc is compiled with g++.
It's rather tricky but it works.
If anyone else have a different idea i'll be happy to change my approach.
Cheers,

Al

[James Kuyper]

abasili wrote:

Ian Collins wrote:

>>
It does if you follow all the points. The first two are often
overlooked.

Here is my Makefile

>>
How are you building your executable?

Here is my Makefile

As Ian said, the first two points are often overlooked, and your
makefile has violated both of them. You compile main() with C instead of
C++, and you use the C compiler rather than the C++ compiler to link the
modules together.

Note: it would have been better to post this message to comp.lang.c++.
The ability to link C code with C++ is defined as part of the C++
standard. The C standard says nothing about that capability. You'll find
more people in that group who can help you than you can find in this group.

[James Kuyper]

abasili wrote:
....

#indef __cplusplus

That should be #ifdef

//mylib.cc

#include <iostream>
#include "mylib.h"

using namespace std; // don't know what for!

For cout, of course. Without that using statement, you'd have to refer
to std::cout.

void foo(){
cout<<"Hello World!\n";
}

[CBFalconer]

abasili wrote:

Ian Collins wrote:

>It does if you follow all the points. The first two are often
overlooked.

I'm sorry about that, actually compiling with g++ the main works.
The main problem is that my C program cannot be compiled with g++,
there are too many incompatibiliti es and a lot of work has been
already done in C. So I have to find another way to call a C++
function through my C code.

In general, you just can't do that. C++ function names are
normally altered by the C++ compiler for various reasons. C
function names are not. So the C system can't link the C++ code.

--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home .att.net>
Try the download section.

[jameskuyper]

CBFalconer wrote:

abasili wrote:

Ian Collins wrote:

It does if you follow all the points. The first two are often
overlooked.

I'm sorry about that, actually compiling with g++ the main works.
The main problem is that my C program cannot be compiled with g++,
there are too many incompatibiliti es and a lot of work has been
already done in C. So I have to find another way to call a C++
function through my C code.

In general, you just can't do that. C++ function names are
normally altered by the C++ compiler for various reasons.

True, but extern "C" turns that off. The only part of his program
compiled with the C++ compiler is a function declared with extern "C".

C
function names are not. So the C system can't link the C++ code.

That may be true; but not for the reason given.

[Stephen Sprunk]

abasili wrote:

Ian Collins wrote:

>It does if you follow all the points. The first two are often
overlooked.

I'm sorry about that, actually compiling with g++ the main works.
The main problem is that my C program cannot be compiled with g++, there
are too many incompatibiliti es and a lot of work has been already done
in C.
So I have to find another way to call a C++ function through my C code.

Always compile C++ source files with a C++ compiler.
Always compile C source files with a C compiler.
If you have a mix of object files from the two languages, use the C++
compiler's linker.

Problem solved.

S