Problem With Semaphores in Linux

nickthegreek82 · 12-22-2002, 07:37 AM

I have written this small program but i take a strange error from gcc compiler

#include <semaphore.h>
extern int errno;
main()
{
sem_t sp;
int retval;
retval=sem_init(&sp,0,2);
if(retval!=0)
{
perror("Couldn't initialize.");
exit(3);
}
}
When i try to complile it,gcc says :
/tmp/ccwEPiIp.o: In function `main':
/tmp/ccwEPiIp.o(.text+0x1c): undefined reference to `sem_init'
collect2: ld returned 1 exit status

Any ideas ? thanks

acid_kewpie · 12-22-2002, 07:40 AM

how are you using gcc? you'ev probably not set to link the semaphore linbrary, whatever it's actually called. add -lsem or whatever it should be.

cybercop12us · 12-22-2002, 08:41 AM

i think u need to do like what chris says gcc -o eg -lrt eg.c

see the man page synopsis for lib to link with gcc

nickthegreek82 · 12-22-2002, 09:24 AM

thanks for your help but now the problem i have is to intentify which library i need to link ... but i think oi will find it out soon

cybercop12us · 12-23-2002, 08:02 AM

see the man page for sem_init . in that under synopsis you should be having something like cc -lrt or -lsem something...

nickthegreek82 · 12-28-2002, 11:10 AM

I still haven't found the library i need , i searched to all man and info pages and there is nothing...If anyone knows the right lib ,please post a message...

Thanks

Morpheus · 12-30-2002, 10:03 PM

hi...
do u really wanna use these semaphores ??
there are another set of semaphores defined in the systemv

u could get info on them by the man pages on semop,semctl,semget

these r preety simple and have been used