c 编程 shmat ( ) 权限被拒绝

Question

我在运行代码时遇到问题。我的 shmat 失败并打印权限被拒绝。我在谷歌上搜索了如何解决它，但我不能。我的代码如下:

#include <stdio.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>
#define ERROR -1

int main ( int argc, char *argv[] ) {
    int shmid,key=50;
    int *val;
    int *x;
    int rw = -1;

    // 0 for write and 1 for read 

    shmid = shmget ( key, sizeof( int ), IPC_CREAT );

    if ( shmid == -1 ) {
        perror ( "Error in shmget\n" );
        return ( ERROR );
    }

    val = ( int * ) shmat ( shmid, NULL, 0 );

    if ( val == -1 ) {
        perror ( "Error in shmat\n" );
        return ( ERROR );
    }

    scanf ( "%d", &rw);

    while ( rw >= 0 ) {
        if ( rw == 0 ) {
            //write in the shared memory
            x = ( int * ) malloc ( sizeof ( int ) );

            if ( x == NULL ) {
                perror ( "Error in malloc" );
                return ( ERROR );
            }

            scanf ( "%d", x );

            val = x;

        }
        else {
            // read from the shared memory
            if ( rw == 1 ) {
                printf ( "%d\n", *val );
            }
        }

        scanf ( "%d", &rw );
    }

    return ( 0 );

}

在这段代码中，我想测试共享内存。当我给 rw = 1 时，我在共享内存中写入一个整数，否则我读取共享内存的值，然后打印该值。我找不到问题出在哪里....

Answer 1

您创建了权限设置为 0000 的共享内存段:

shmid = shmget ( key, sizeof( int ), IPC_CREAT );

应该是

shmid = shmget ( key, sizeof( int ), IPC_CREAT | 0660 );

或类似的。