shmat返回带有errno = 13(EACCES)的细分falut [英] shmat returns segmentation falut with errno=13(EACCES)

问题描述

我只想测试shmget()和shmat()，但似乎有些问题. :(

I just want test shmget() and shmat() , but something seems wrong. :(

shmget()效果很好，但是shmat()导致分段错误.

shmget() works well but shmat() causes segmentation fault.

这是代码:

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

int main(void)
{
    key_t key=98;/* yes, just 98 for test */
    int shid;
    char *str=NULL;
    shid = shmget(key, 4096, IPC_CREAT);
    printf("shid:%d\n",shid);
    str=(char*)shmat(shid,NULL,0);
    printf("str:%d\n",(int)str);
    printf("errno:%d\n", errno);
    str[0] = 'h';
    str[1] = '\0';

    return 0;
}

这是输出:

shid:28246036
str:-1
errno:13
zsh: segmentation fault  ./t1

thx:D

推荐答案

您必须在开始时定义_SVID_SOURCE或_XOPEN_SOURCE

You must define _SVID_SOURCE or _XOPEN_SOURCE at the very begin

#define _SVID_SOURCE
#include <stdlib.h>
#include <sys/ipc.h>
...

使用ftok()

key_t key= ftok("demo.c", 'R');

因为未设置PERMS，它会返回errno 13:

It returns errno 13 because you don't set PERMS:

shid = shmget(key, 4096, IPC_CREAT);

必须

shid = shmget(key, 4096, 0777 | IPC_CREAT);

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