Question

I am running into a problem when I run my a.out file using the ./a.out command. I am getting segmentation code error number 11. I am getting a segmentation fault when trying to access sharedMemory. I use memcpy to paste the data into shared memory. It is Segmentation fault 11.

Am I accessing the memory correctly?

#include<stdio.h>
#include<sys/types.h>
#include<sys/shm.h>
#include<sys/ipc.h>
#include<unistd.h>
#include<time.h>
int main(){
    pid_t childPid;
    childPid = fork();
    char *shm;
    if(childPid == 0){
        char *args[] ={"ls","-l",NULL};
        int shmid;
        int shsize = 100;
        key_t key;
        char *s;
        key = 9876;
        shmid = shmget(key,shsize, IPC_CREAT | 0666);
        if(shmid < 0){
            printf("error getting shmid");
            exit(1);
        }

        shm = shmat(shmid,NULL,0);
        if(shm == (char *) -1){
            printf("error getting shared memory");
            exit(1);
        }
        time_t startTime;
        gettimeofday(&startTime,0);
        memcpy(shm,&startTime,sizeof(startTime));
        time_t endTime;
        execvp(args[0],args);
        printf("successfuly created child proceess");
        exit(0);
    }

    else if (childPid <0){
        printf("unsuccessfuly created child proccess");



        else{
            int returnStatus;
            waitpid(childPid,&returnStatus,0);
            if(returnStatus == 0){
                printf("The child terminated normally");
                printf("%s",*shm);
            }

            if(returnStatus == 1){

                printf("The child terminated with error");
            }
        }

    }
}

Answer 1

在

    time_t startTime;
    gettimeofday(&startTime,0);

gettimeofday 的第一个参数必须是struct timeval *而不是time_t *

如此

    struct timeval startTime;
    gettimeofday(&startTime,0);

在

char *shm;
...
printf("%s",*shm);

您不得取消引用 shm ，因为当前其第一个字符的ascii代码用作字符串的地址，

char *shm;
...
printf("%s",shm);

之后

else if (childPid <0){
    printf("unsuccessfuly created child proccess");

缺少}

我鼓励您进行编译，要求编译器产生警告，并使用 gcc 使用选项-pedantic -Wall

Segmentation fault 11 trying to get data after using memcpy

1 个答案: