c - 段错误(核心转储)-我的代码出了什么问题

Question

有人知道为什么我收到消息“段错误(核心已转储)”吗？怎么了？在我看来，问题出在数组上。我知道“段错误”意味着我试图访问我无权访问的内存。

#include <stdio.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/types.h>
#include <unistd.h>

int main(int argc, const char* argv[])
{
    int shmid;
    int i, j;
    int glos;
    pid_t pid;
    key_t key;
    long *wyniki;

    key = ftok("/home/sebastian", 2);

    shmid = shmget(key, 20 * sizeof(long), IPC_CREAT);

    if (shmid == -1) {
        printf("Error - New memory segment");
    }
    else {
        printf("My memory segment: %d\n", shmid);
        wyniki = (long*) shmat(shmid, 0, 0);

        for (i = 0; i < 5; i++) {
            wyniki[i] = 0;
        }

        // Creating new processes
        for (i = 0; i < 20; i++) {
            pid = fork();
            if (pid == 0) {
                srand48(time(NULL) + getpid());
                for (j = 0; j < 1000000; j++) {
                    glos = rand() % 5;
                    wyniki[glos] += 1;
                }
            }
            else {
                printf("ERROR - PROCESSES");
            }
        }
    }

return 0;
}

Answer 1

您创建共享内存段时没有正确设置权限位，因此您无权访问该内存。

根据 shmget() man page :

   int shmget(key_t key, size_t size, int shmflg);
   ...
   In addition to the above flags, the least significant 9 bits of
   shmflg specify the permissions granted to the owner, group, and
   others.  These bits have the same format, and the same meaning, as
   the mode argument of open(2).  Presently, execute permissions are not
   used by the system.

您需要指定共享内存段的权限:

shmid=shmget(key, 20 * sizeof(long), IPC_CREAT | 0600);

或者使用0640、0660或符号模式。

但首先您可能必须使用 ipcrm 删除现有段。