Question

#include<pthread.h>
#include<stdio.h>
#include<sys/stat.h>
#include<errno.h>

#define SIZE 3

/***I'm trying to send name of each file in a thread and trying to receive their respective size in main *******/

void *doit(void *name)
{
        int *size;
        struct stat st;
        char temp_name[30];
        memset(temp_name, '\0', sizeof(temp_name));
        strcpy(temp_name, (char *)name); //type casted
        stat(temp_name, &st);
        *size = st.st_size; //calculated the size

        printf("File name is: %s\n", temp_name);
        printf("File size is: %d\n", *size);
        pthread_exit((void *)size); //exited from thread
}

int main(int argc, char *argv[])
{
        pthread_t th_id[SIZE];
        int ret_val;
        int i;
        void **size[SIZE];
        for(i=0; i<SIZE;i++)
        {
                size[i] = (void **)malloc(30*sizeof(void *)); //allocated memory to void double pointer
                if(size[i] == NULL)
                {
                        printf("Memory not allocated to %dth member of size\n", (i+1));
                }
        }
        for(i=0; i<3; i++)
        {
          /*****Creating Thread**********/
                ret_val = pthread_create(&th_id[i], NULL, &doit, (void *)argv[1+i]);
                if(ret_val != 0)
                {
                        perror("Thread creation error\n");
                        exit(0);
                }
                pthread_join(th_id[i], size[i]);
                printf("Size is %d\n",**(int **)size[i]); //typecasted and printed
        }
        pthread_exit(NULL);
        return 0;
}

在这个程序中，我在第一次调用pthread_join后出现分段错误。当传递第一个文件时，我在main中获得了合适的大小。但在调用第二个文件时，我遇到了分段错误。使用gdb我得到的是“** size [1]和** size [2]尽管是malloc但仍然为NULL。但是在main的开头，我在分配内存时没有收到错误信息。它应该意味着记忆最初分配。请帮我解决。

Answer 1

    int *size;
    struct stat st;
    char temp_name[30];
    memset(temp_name, '\0', sizeof(temp_name));
    strcpy(temp_name, (char *)name); //type casted
    stat(temp_name, &st);
    *size = st.st_size; //calculated the size

您正在取消引用未经初始化的指针。你永远不会让size指向任何东西。

从C中的多个线程接收值

1 个答案: