Problems #including K&R function prototypes from C++

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3 total messages Started by Max Welton Mon, 27 Nov 1995 19:46

#845

Author: Max Welton
Date: Mon, 27 Nov 1995 19:46

50 lines
1749 bytes

I'm attempting to use g++ 2.7.1 with a combination of 
our own C++ and various vendor's C. When a #included
header contains a K&R style function prototype, g++ 
is unable to parse it (see below). The HP C++ cfront
compiler handles the same code with a warning (again, 
see below).

We have found nothing in the gcc/g++ man-pages that
addresses this problem and are not in a position to
edit the third-party header files. We would very much
like to use g++ (for various reasons). Have I overlooked
something obvious?

$ cat foo.h
#ifndef foo_h
#define foo_h
int foo(boo)
   int boo;
{
   return boo;   
}
#endif

$ cat main.C
#include <iostream.h>
extern "C" {
#include "foo.h"
}
int main()
{
   cout << "Hello" << endl;
   return foo(0);
}

$ g++ -c main.C
main.C:4: `boo' was not declared in this scope
main.C:5: parse error before `int'
main.C:6: parse error before `{'

Compilation exited abnormally with code 1 at Mon Nov 27 11:26:24

CC -c main.C
CC: "main.C", line 4: warning: old style definition of foo() (anachronism)
(1386)

Compilation finished at Mon Nov 27 11:35:38
--
Max Welton, CMST (Coordinator of Many Small Things)
   maxw@lmsc.lockheed.com
   maxw@ix.netcom.com

Re: Problems #including K&R function prototypes from C++

#846

Author: Shekar Ramanathan
Date: Mon, 27 Nov 1995 21:23

60 lines
1851 bytes

Max Welton (maxw@lmsc.lockheed.com) wrote:
[snip]
> We have found nothing in the gcc/g++ man-pages that
> addresses this problem and are not in a position to
> edit the third-party header files. We would very much
> like to use g++ (for various reasons). Have I overlooked
> something obvious?

Yes.  You should have only function *prototypes*, not function definitions,
inside extern "C" (see FAQ).

> $ cat foo.h
> #ifndef foo_h
> #define foo_h
> int foo(boo)
>    int boo;
> {
>    return boo;   
> }
> #endif

> $ cat main.C
> #include <iostream.h>
> extern "C" {
> #include "foo.h"
> }
> int main()
> {
>    cout << "Hello" << endl;
>    return foo(0);
> }

What you should do is have another file called foo.c and compile it using
a K&R C compiler.  In main.C, you should just include a prototype declaration
for foo and finally link them together.

foo.c
int foo(boo)
    int boo;
{
   return boo;   
}

main.C:

extern "C"{
	int foo();
}
int main()
{ cout << foo(0) << endl; }


Shekar

--
---------------------------------------------------------------------
Shekar Ramanathan              |   mailto:shekar@CS.MsState.edu
Department of Computer Science |   http://www.cs.msstate.edu/~shekar
Mississippi State University   |
---------------------------------------------------------------------

Re: Problems #including K&R function prototypes from C++

#841

Author: Max Welton
Date: Tue, 28 Nov 1995 00:11

44 lines
1695 bytes

shekar@gizmo.cs.msstate.edu (Shekar Ramanathan) wrote:
>Max Welton (maxw@lmsc.lockheed.com) wrote:
[snip]
>What you should do is have another file called foo.c and compile it using
>a K&R C compiler.  In main.C, you should just include a prototype declaration
>for foo and finally link them together.
>
>foo.c
>int foo(boo)
>    int boo;
>{
>   return boo;   
>}
>
>main.C:
>
>extern "C"{
>	int foo();
>}
>int main()
>{ cout << foo(0) << endl; }
>
>
>Shekar

I have the same problem with or without the 'extern"C"'. In the 
real-world case, "foo.h" is a 3rd-party vendor header. We're just 
not in a position to rewrite our favorite vendor's K&R headers.

I was hoping that g++ could be cajoled somehow into the behaviour 
of our HP cfront compiler in this case:

  CC -c main.C
  CC: "main.C", line 4: warning: old style definition of foo() (anachronism) 
  (1386)

  Compilation finished at Mon Nov 27 11:35:38

Not there yet...

--
Max Welton, CMST (Coordinator of Many Small Things)
   maxw@lmsc.lockheed.com
   maxw@ix.netcom.com

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