如何从C中的pthread线程返回值? [英] How to return a value from pthread threads in C?

问题描述

我是C语言的新手，并且想玩一些线程.我想使用 pthread_exit()

I'am new to C and would like to play with threads a bit. I would like to return some value from a thread using pthread_exit()

我的代码如下:

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

void *myThread()
{
   int ret = 42;
   pthread_exit(&ret);
}

int main()
{
   pthread_t tid;
   void *status;

   pthread_create(&tid, NULL, myThread, NULL);
   pthread_join(tid, &status);

   printf("%d\n",*(int*)status);   

   return 0;
}

我希望程序输出"42 \ n"，但它输出一个随机数.如何打印返回的值?

I would expect the program output "42\n" but it outputs a random number. How can I print the returned value?

根据第一个答案，问题是我正在返回指向局部变量的指针.返回/存储多个线程的变量的最佳实践是什么?全局哈希表?

According to first answers the problem is that I am returning pointer to local variable. What is the best practice of returning/storing variables of multiple threads? A global hash table?

预先感谢

推荐答案

您正在返回局部变量的地址，该局部变量的地址在线程函数退出时不再存在.无论如何，为什么要调用pthread_exit?为什么不简单地从线程函数返回值?

You are returning the address of a local variable, which no longer exists when the thread function exits. In any case, why call pthread_exit? why not simply return a value from the thread function?

void *myThread()
{
   return (void *) 42;
}

然后在主目录中:

printf("%d\n",(int)status);   

如果需要返回一个复杂的值(如结构)，则最简单的方法是通过malloc()动态分配它并返回一个指针.当然，启动线程的代码将负责释放内存.

If you need to return a complicated value such a structure, it's probably easiest to allocate it dynamically via malloc() and return a pointer. Of course, the code that initiated the thread will then be responsible for freeing the memory.

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