从Linux上的消息队列中读取时出错"Bad address"

Question

当我需要编写简单的时间服务器和使用Linux消息队列的客户端时,我有分配.服务器打开一个消息队列,客户端发送一个带有PID的消息(类型为1的消息),服务器读取该消息并发送一个PID类型的消息(取自读取的消息).我把所有代码都放在下面,因为我不知道我在哪里弄错了.我不是Linux编程专家.甚至不知道我写的服务器是否正确.

服务器和客户端包含的文件(我需要以这种方式编写).

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <sys/msg.h>
#include <sys/ipc.h>
#include <sys/types.h>
#include <string.h>
#include <signal.h>

#define QUEUE 100
#define PERM_ALL 0777

typedef struct my_msgbuf {
    long mtype;
    int pid;
} ClientMessage;

typedef struct my_msgbuf2 {
    long mtype;
    struct tm time;
} TimeMessage;

服务器

int m_queue;

void cleanup(int signum) {
    if (msgctl(m_queue, IPC_RMID, NULL) == -1) {
        printf("Something happen on clean up\n");
        exit(1);
    }
    exit(signum);
}

int main() {
    ClientMessage pid_message;
    TimeMessage t;
    time_t clock;
    struct tm *cur_time;

    if ((m_queue = msgget(QUEUE, PERM_ALL | IPC_CREAT)) == -1) {
        printf("Can't create and open message queue\n");
        exit(1);
    }
    printf("created message queue = %d\n", m_queue);
    fflush(stdout);
    //t = malloc(sizeof(TimeMessage));
    signal(SIGINT, cleanup);

    while (1) {
        if (msgrcv(m_queue, &pid_message, sizeof(pid_message.pid), 1, 0) == -1) {
            break;
        } else {
            t.mtype = pid_message.pid;
            clock = time(NULL);
            cur_time = localtime(&clock);
            memcpy(&t.time, cur_time, sizeof(struct tm));
            msgsnd(m_queue, &t, sizeof(struct tm), 0);
        }
    }

    cleanup(0);
}

客户

int main() {
    int m_queue;
    TimeMessage *t;
    ClientMessage client;

    if ((m_queue = msgget(QUEUE, PERM_ALL)) == -1) {
        perror("Error in opening queue");
        exit(1);
    }

    client.mtype = 1;
    client.pid = getpid();

    while (1) {
        if (msgsnd(m_queue, &client, sizeof(client.pid), 0) == -1) {
            perror("Error sending to queue");
            exit(1);
        } else {
            if (msgrcv(m_queue, t, sizeof(struct tm), client.pid, 0) == -1) {
                perror("Error reading from queue");
                exit(1);
            }   
            printf("time: %d:%d:%d\n", t->time.tm_hour, t->time.tm_min, t->time.tm_sec);
        }
    }
    return 0;
}

两个程序编译没有错误,但客户端返回"错误从队列读取"msgrcv返回-1.

Answer 1

添加之后perror,似乎您已经收到错误说明"Bad Address"(EFAULT),这意味着" msgp(缓冲区)指向的地址不可访问".从代码中可以看出,没有分配内存,TimeMessage *t因此您可以分配内存或只是将其更改为TimeMessage tand &t而不是tto msgrcv.另外大小应sizeof t(从假设的变化*t来t,或sizeof(TimeMessage)对*t),而不是sizeof(struct tm)(显然,你会改变printf相应语句)
希望这有助于!