Question

以下是我的代码。我正在尝试让main_thread获取用户输入，存储在global_variable中，然后打印出来。但是，在获得输入后，我的打印输出是Segmentation Fault。有人有任何想法吗？

#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>

char* global_variable;

void *first_thread(void *ptr) {
    printf("%s \n", (char *)ptr);
    pthread_exit(NULL);
}

void *second_thread(void *ptr) {
    printf("%s \n", (char *)ptr);
    pthread_exit(NULL);
}

void *third_thread(void *ptr) {
    printf("%s \n", (char *)ptr);
    pthread_exit(NULL);
}

void *main_thread() {

    printf("Thread 1: Please enter a line of text [Enter \"Exit\" to quit]\n");
    fgets(global_variable, 999, stdin);
    printf("%s", global_variable);

    pthread_exit(NULL);
}

int main () {

    pthread_t t_m, t1, t2, t3;

    //const char *m1 = "Thread 1", *m2 = "Thread 1", *m3 = "Thread 3";

    int cr1, cr2;

    //creating threads
    cr1 = pthread_create(&t_m, NULL, main_thread, NULL);
    //cr1 = pthread_create(&t1, NULL, first_thread, NULL);
    //cr1 = pthread_create(&t2, NULL, second_thread, NULL);
    //cr1 = pthread_create(&t3, NULL, third_thread, NULL);
    //threads created

    pthread_join(t_m, NULL);

    printf("Global Variable: %s", global_variable);

    exit(0);
    return 0;
}

Answer 1

注意声明：

char* global_variable;

不是数组而是指针，您尝试读取为：

fgets(global_variable, 999, stdin);

不分配内存==＆gt;未定义的行为，是运行时分段错误的原因。

要纠正它，要么为@dutt在answer中建议分配内存，要么global_variable应该是一个数组char global_variable[1000];

Answer 2

您没有为global_variable分配内存，因此fgets尝试在内存中的随机位置写入，导致操作系统检测到内存冲突并通过发送导致分段错误的SIGSEGV来停止进程

将您的主要内容更改为以下内容：

 int main () {

  pthread_t t_m, t1, t2, t3;
  global_variable = malloc(sizeof(char)*999);
  //const char *m1 = "Thread 1", *m2 = "Thread 1", *m3 = "Thread 3";

 ...more code...

 printf("Global Variable: %s", global_variable);
 free(global_variable);

阅读malloc()和free()

C编程pthread打印分段故障

2 个答案: