分段错误（核心转储） - 我的代码有什么问题

Question

有人知道我为什么会收到“分段错误（核心转储）”消息吗？怎么了？在我看来，问题出在数组上。我知道“分段错误”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

修复“创建的进程过多”问题：

改变这个：

    // 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");
        }
    }

到这里：

    // Creating new processes
    for (i = 0; i < 20; i++) 
    {
        pid = fork();
        if (pid == 0) 
        { // child process
            srand48(time(NULL) + getpid());
            for (j = 0; j < 1000000; j++) 
            {
                glos = rand() % 5;
                wyniki[glos] += 1;
            }
            exit();
        }

        else if( 0 > pid)
        { // error occurred
            perror( "fork() failed" );
            printf("ERROR - PROCESSES\n");
        }

        //else
        //{ // parent process
        //    ; 
        //}
    } // end: for 20 child processes

Answer 2

您在未正确设置权限位的情况下创建了共享内存段，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.

需要指定共享内存段的权限：

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

或使用0640、0660 或符号模式。

但首先您可能必须使用 ipcrm 删除现有段。