Consumer-Producer problem - c

Question

I am having a problem with my Consumer, producer program, it seems to load, but returns a segmentation error. I have tried everything to fix it but still failing!! Will be greatful for any assistance.
Note; The code is really much, semaphore.h code is within, if anyone wishes to test. and the rest of the code is as is here. Am runing this on a Unix machine.
//----------------SEMOPHORE.H--------------------------
/*********************** semaphore.h ****************************/
#define SEM_NAME "semaphore.h",'a'
#define SEM_MAX 3
#define FREE 0
#define DATA 1
#define ROOM 2
#define S_WAIT -1
#define S_SIGNAL 1
#define NO_EVENT -1
int sem_config(int, int);
int sem_wait(int, int);
int sem_signal(int, int);
//----------------Producer-----------------------
#include<stdio.h>
#include"semaphore.h"
#include"shbuf.h"
# include <string.h>
# include "shbuf.h"
void myadd();
main()
{
sem_config(DATA, FREE);
myadd();
sem_signal(DATA,S_SIGNAL);
return 0;
}
void myadd()
{
char str[80];
char discard;
printf("you can type a message for the producer."\n);
printf("Producing message : ");
scanf("%s%c", str, &discard);
q_add(strlen(str) , str);
}
//---------------------------CONSUMER---------------------------
#include<stdio.h>
#include"semaphore.h"
#include"shbuf.h"
# include <string.h>
# include "shbuf.h"
void myremove();
main()
{
sem_wait(DATA, S_WAIT);
myremove();
sem_signal(DATA,S_SIGNAL);
return 0;
}
void myremove()
{
char str[80];
if(q_items() > 0)
{
q_remove(1 , str);
str[1] = 0;
printf("%s\n", str);
}
}
//-------------------------------SEMAPHORE.C--------------------------------------
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include "semaphore.h"
static int sem_id;
static union semun
{
int val; /* value for SETVAL */
struct semid_ds *buf; /* buffer for IPC_STAT & IPC_SET */
ushort array[1]; /* array for GETALL & SETALL, used in setting or retrieving all semaphorevalues in a set.*/
} sem_attr;
static struct sembuf asem[1];
static key_t s_key; //key for shared memory
int sem_config(int event, int init_val)
{
int x;
s_key = ftok(SEM_NAME); //key for semaphore
//create a semaphore for process synchronization
if ( -1 == (sem_id = semget(s_key, SEM_MAX, 0666|IPC_CREAT ) ))
{
perror("semget");
return -1;
}
if ( event == NO_EVENT )
return 0; /*locate semaphore only*/
//set initial value of semaphore
sem_attr.val = init_val;
if ( -1 == semctl(sem_id, event, SETVAL, sem_attr ) )
{
perror("semctl SETVAL");
return -1;
}
if ( -1 == ( x = semctl(sem_id, event, GETVAL, sem_attr ) ) )
{
perror("semctl GETVAL");
return -1;
}
assert( x == init_val );
return 0;
}
int sem_wait(int event, int nwaits)
{
asem[0].sem_num = event;
asem[0].sem_op = nwaits * S_WAIT;
asem[0].sem_flg = 0;
if ( event == NO_EVENT ) /*remove semaphore set*/
if ( -1 == semctl(sem_id, 0, IPC_RMID, sem_attr ) )
{
perror("semctl IPC_RMID");
return -1;
}
else
return 0;
if ( -1 == semop(sem_id, asem, 1 ) )
{
perror("semop");
return -1;
}
return 0;
}
int sem_signal(int event, int nsignals)
{
asem[0].sem_num = event;
asem[0].sem_op = nsignals * S_SIGNAL;
asem[0].sem_flg = 0;
if ( event == NO_EVENT )
if ( -1 == semctl(sem_id, 0, IPC_RMID, sem_attr ) )
{
perror("semctl IPC_RMID");
return -1;
}
else
return 0;
if ( -1 == semop(sem_id, asem, 1 ) )
{
perror("semop");
return -1;
}
return 0;
}

Answer 1

In general, the best way to debug segmentation faults is by compiling with the -g flag and running in a debugger like gdb. It will tell you exactly where it is crashing and let you print out the values of variables to tell you why.

Answer 2

Compile with debugging symbols. If you're using gcc then use the -g3 flag for the most symbols. You should also be using the -Wall flag and pay attention to the warnings it gives you. Try stepping trough the program that fails first with a debugger and see where it fails.
My bet is that the problem is in your q_remove and q_add code because that's the code you left out, and because it probably uses arrays.