Invoking c function in a c plus plus function...

[Rahul]

Hi Everyone,

I want to invoke a c function ( object file created by cc ) from a
cpp function ( object file is created using g++ ). When i try to link,
both the object files using g++

g++ cfile.o cppfile.o

i get an error saying,

: undefined reference to `fun()'
collect2: ld returned 1 exit status

Note that the fun() is the c function defined in cfile.c. I can't use
cc to link both the object files as the master file is a cpp source
file.

Is there anyway to get this done? I know the method of using extern
"C" but that works only when a cpp function ( object file created in g+
+ ) is to be invoked from a c function ( object file created in cc ).

Thanks in advance ! ! !

[Gianni Mariani]

Re: Invoking c function in a c plus plus function...

Rahul wrote:

Hi Everyone,
>
I want to invoke a c function ( object file created by cc ) from a
cpp function ( object file is created using g++ ). When i try to link,
both the object files using g++
>
g++ cfile.o cppfile.o
>
i get an error saying,
>
: undefined reference to `fun()'
collect2: ld returned 1 exit status
>
Note that the fun() is the c function defined in cfile.c. I can't use
cc to link both the object files as the master file is a cpp source
file.
>
Is there anyway to get this done? I know the method of using extern
"C" but that works only when a cpp function ( object file created in g+
+ ) is to be invoked from a c function ( object file created in cc ).

I believe that's exactly what extern "C" is for. Show us the
chunk-o-code that exhibits this problem.

[Rahul]

Re: Invoking c function in a c plus plus function...

On Mar 24, 4:47 pm, Gianni Mariani <gi4nos...@mari ani.wswrote:

Rahul wrote:

Hi Everyone,

>

I want to invoke a c function ( object file created by cc ) from a
cpp function ( object file is created using g++ ). When i try to link,
both the object files using g++

>

g++ cfile.o cppfile.o

>

i get an error saying,

>

: undefined reference to `fun()'
collect2: ld returned 1 exit status

>

Note that the fun() is the c function defined in cfile.c. I can't use
cc to link both the object files as the master file is a cpp source
file.

>

Is there anyway to get this done? I know the method of using extern
"C" but that works only when a cpp function ( object file created in g+
+ ) is to be invoked from a c function ( object file created in cc ).

>
I believe that's exactly what extern "C" is for. Show us the
chunk-o-code that exhibits this problem.

cfile.c

int fun()
{
return (0);
}

cppfile.cpp

#include <cstdio>

extern int fun();

int main()
{
int a = fun();
printf("integer is %d\n",a);
}

extern "C" just avoids name mangling. Are you suggesting to have it
around the function call in main() of cppfile.cpp?

[Andrey Tarasevich]

Re: Invoking c function in a c plus plus function...

Rahul wrote:

>
By the way, this is working,
>
cppfile.cpp
>
#include <cstdio>
>
extern "C"
{
extern int fun();
>
int main()
{
int a = fun();
printf("integer is %d\n",a);
}
}
>

'extern "C"' is supposed to be applied to declarations. There's no much point in
wrapping your entire translation unit into 'extern "C"'

extern "C" int fun();

int main()
{
int a = fun();
printf("integer is %d\n",a);
}

--
Best regards,
Andrey Tarasevich

[James Kanze]

Re: Invoking c function in a c plus plus function...

On Mar 24, 2:45 pm, Andrey Tarasevich <andreytarasev. ..@hotmail.com>
wrote:

Rahul wrote:

By the way, this is working,

cppfile.cpp

#include <cstdio>

extern "C"
{
extern int fun();

int main()
{
int a = fun();
printf("integer is %d\n",a);
}
}

'extern "C"' is supposed to be applied to declarations.
There's no much point in wrapping your entire translation unit
into 'extern "C"'

It's frequent to wrap a set of declarations (or even an entire
header file) in `extern "C"'---there are even some types of
declarations (e.g. typedef's) which can't be done otherwise.

On the other hand, I'm not too sure that declaring main to be
`extern "C"' is legal. (If it is, the `extern "C"' is ignored.)
In the OP's case, applying the `extern "C"' to just the
declaration is quite appropriate.

extern "C" int fun();

And of course, this really belongs in a separate header file.

--
James Kanze (GABI Software) email:james.kan ze@gmail.com
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