c - 尝试复制共享内存地址时出现段错误

Question

#include<stdio.h>
#include<fcntl.h>
#include<unistd.h>
#include<sys/ipc.h>
#include<sys/shm.h>
#include<string.h>
#include<malloc.h>

int main(int argc,char* argv[]){
    /* Initialise the variables */
    int key,shmid,fd1,bytes_written;
    char *shmptr = NULL;
    char *buff = NULL;
    key = shmid = fd1 = bytes_written = 0;

    /*Validate the i/p parameter*/
    if(argc < 2){
        printf("Enter the Output file");
        return -1;
    }
    printf("\n The Output File is : %s \n",argv[1]);

    /* Open the file in write mode */
    fd1 = open(argv[1],O_WRONLY);
    if(fd1 == -1){
        printf("\n File cannot be opened!  \n");
        return -1;
    }

    /* Create the shared memory key */
    key = ftok(".",12);

    /* create the shared memory segment */
    shmid = shmget(key,1000,0);

    /* Attach with the shared memory segment
    ** get the pointer to the shared address
    */
#if 0
    buff = (char *)malloc((sizeof(char) * 1000));
    if(NULL == buff){
    printf("\n Unable to allocate the memory! \n");
    return -1;
}
#endif

    shmptr = shmat(shmid,0,0);
    buff = shmptr;
    //memcpy(buff,shmptr,1000);
    printf("\n %s \n",buff);

    /* Write the contents into the file */
    bytes_written = write(fd1,buff,1000);
    if(bytes_written == -1){
        printf("\n Write operation is not successfull! \n");
        return -1;
    }

    /* Detach from the shared memory */
    shmdt(shmptr);
    //free(buff);

    return 0;
}      

我想将共享内存中的内容复制到缓冲区，然后将数据写入文件。当我尝试执行 buff = shmptr;

时遇到段错误

Answer 1

验证您的 shmget() 和 shmat() 结果。可能他们返回 -1 并且您尝试访问无效的内存位置。