Very Computer

by **Lars Hagstro** » Tue, 29 Feb 2000 04:00:00

Hi,

I've come across something that I find very odd and I haven't been able to
find any previous questions about it anywhere. I hope it's not a silly question
with an obvious answer.

I've narrowed the problem down to a very simple one.
If I compile the following program with gcc (as a C program) it works
fine.

#include<unistd.h>
int main()
{
return getpgid(0);

Quote:}

But when I compile it with g++ as a C++ program I get this message:
test.cc: In function `int main()':
test.cc:6: implicit declaration of function `int getpgid(...)'

If I do a forward declaration of the getpgid fcn I will get a link error:
/tmp/ccHofd4c.o: In function `main':
/tmp/ccHofd4c.o(.text+0xc): undefined reference to `getpgid(int)'
collect2: ld returned 1 exit status

At least this is the behaviour on Linux distros mandrake 6.1 and 7.0
and debian potato (i think). This is with version 2.95.2.
On a VAX (Ultrix 4.4) with 2.8.1 I get both link error and warning in
c++ and only the link error in c.

On a Sun UltraSparc with SunOS 5.7 (Solaris v??) and gcc 2.95.1 everything
works just fine.

Is this a real bug or am I missing something?

Thanks in advance
Lars

--

by **Thomas Rehlic** » Tue, 29 Feb 2000 04:00:00

> Hi,

> I've come across something that I find very odd and I haven't been able to
> find any previous questions about it anywhere. I hope it's not a silly question
> with an obvious answer.

> I've narrowed the problem down to a very simple one.
> If I compile the following program with gcc (as a C program) it works
> fine.

> #include<unistd.h>
> int main()
> {
> return getpgid(0);
> }

> But when I compile it with g++ as a C++ program I get this message:
> test.cc: In function `int main()':
> test.cc:6: implicit declaration of function `int getpgid(...)'

It seems that GNU-C/C++ is a little bit to perfect. The prototype of getpgid in
unistd.h is enclosed in
#ifdef __USE_XOPEN_EXTENDED ... #endif since this function is a X/Open Unix
extension (?).
Try to compile with -D_XOPEN_SOURCE=500 or -D_GNU_SOURCE and it works.

Thomas

Very Computer

getpgid() won't work in g++!

getpgid() won't work in g++!

getpgid() won't work in g++!