Thread: cyclic buffer

i'm trying to produce a program that stays in a endless loop inserting integers into a cyclic array, and i'm stuck on getting integers into the array can anyone point me in the correct direction? my code so far is:

Code:

#include <stdio.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <string.h>
#include <stdlib.h>
#include <sys/sem.h>
#include <errno.h>
#include <string.h>

#define KEY     (key_t) 12345
#define MUTEX  (key_t) 100
#define PERM 0600

extern int errno;
extern int showsem(key_t);

int initsem(key_t, int);
int p(int);
int v(int);
int mutex;
int OFLO;
int UFLO;
i

struct shseg
{   
   int ptr;
   char buffer[100];
} *ashseg;



int main() 
{
   int shmid;
   shmid=shmget(KEY, sizeof(struct shseg), IPC_CREAT|0666);
   ashseg=(struct shseg *) shmat(shmid, 0, 0); //note type cast
   mutex=initsem(MUTEX,1);
   OFLO=initsem(OFLO,3);
   UFLO=initsem(UFLO,0);
   for (ashseg->ptr=0;ashseg->ptr<strlen(ashseg->buffer); ashseg->ptr++) {
   p(OFLO);
   p(mutex);	
   strncpy(ashseg->buffer, "test string\n", 20);
   putchar(ashseg->buffer[getchar()]);
   v(mutex);
   v(UFLO);	
   sleep(1);}

   killsem(mutex);
   killsem(OFLO);
   killsem(UFLO);
}


int initsem(key_t semkey,int semval)
 {
    int status=0, semid;
     if ((semid=semget(semkey,1,PERM|IPC_CREAT|IPC_EXCL))==-1) 
            if (errno==EEXIST)
                semid=semget(semkey,1,0);}
        else
                status=semctl(semid,0,SETVAL,semval);
       
       if (semid==-1||status==-1) {
           perror("initsem failed");
           return(-1);}

   return(semid);
}

int p(int semid)
{
   struct sembuf p_buf;
   p_buf.sem_num = 0;
   p_buf.sem_op = -1;
   p_buf.sem_flg = SEM_UNDO;

   if (semop(semid, &p_buf, 1) == -1) {
       perror("p(semid) failed");
       exit(1);
        }
      else
      return(0);
 }

int v(int semid)
{
   struct sembuf v_buf;
    v_buf.sem_num = 0;
    v_buf.sem_op = 1;
    v_buf.sem_flg = SEM_UNDO;

        if (semop(semid, &v_buf,1) == -1) {
          perror("v(semid) failed");
          exit(1);
          }
        else
           return(0);
 }

int killsem(semid)
 {
        if (semctl(semid,0,IPC_RMID,0)==-1)
                return(-1);
        return(0);}

your way to place braces is just purely horrble

Code:

int initsem(key_t semkey,int semval)
{
	int status=0, semid;
	if ((semid=semget(semkey,1,PERM|IPC_CREAT|IPC_EXCL))==-1) 
		if (errno==EEXIST)
			semid=semget(semkey,1,0);
}
		else
			status=semctl(semid,0,SETVAL,semval);

			if (semid==-1||status==-1) 
			{
				perror("initsem failed");
				return(-1);
			}

			return(semid);
}