Question

Given this code :

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/wait.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/shm.h>
#include <semaphore.h>
#include <pthread.h>

#define BUF_SIZE 256
int main()
{
    key_t key;
    char *virtualaddr;
    sem_t *get, *put;
    int shmid;

   const char* messageOne = "Hello world , I'm child number 1\n";
   const char* messageTwo = "Hello world , I'm child number 2\n";

   char buf[BUF_SIZE];

   key = ftok("anyfile",'R');

  shmid = shmget(key,1024,0644|IPC_CREAT);
...
...
shmctl (shmid, IPC_RMID, NULL);
exit(EXIT_SUCCESS);
}

I get from eclipse undefined reference to sem_open .

I’ve check with this post since this question is very similar to mine , but didn’t understand exactly where is my mistake ,

Can you please explain where do I need to fix it / add another compilation command (if this is indeed the case) ?

Much appreciated

Answer 1

You need to include -lpthread when compiling. This is used by the linker, to link your binary against the library.

The other answers already cover how to do this on the command line.

To do this in Eclipse, you need to follow the directions here:

In the project properties, go to : C/C++ Build –> Settings. Then
“Tool Settings”, select “Libraries” under “Linker”. You can add all
your project libraries there (without the “-l”). Also in the lower
part, you can add custom path to search libraries