c - Linux，C : how can I get return value from thread which greate than 4G in a 32bits OS?

Question

我正在运行 32 位 操作系统。现在我创建的线程将返回一个int值，它可能大于4G​​。如何通过 pthread_join() 从我的 main() 函数接收此值？看起来在 32 位 系统中，(void *) 是 4 个字节。

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

void* thread_function(void)
{
    uint64_t nbytes  = 0;
    //assign values to nbytes, it could be larger than 4G.
    return (void *)nbytes;
}

int main()
{
    pthread_t thread_id;
    uint64_t nbytes;

    pthread_create (&thread_id, NULL, &thread_function, NULL);
    pthread_join(thread_id,(void**)&nbytes); 
}

Answer 1

像这样:

void* thread_function(void *)
{
    uint64_t nbytes  = 0;
    //assign values to nbytes, it could be larger than 4G.

    void *retval = malloc (sizeof (nbytes));
    memcpy (retval, &nbytes, sizeof (nbytes));
    return retval;
}

int main()
{
    pthread_t thread_id;
    uint64_t nbytes;

    pthread_create (&thread_id, NULL, &thread_function, NULL);

    void *ret;
    pthread_join(thread_id, &ret); 
    memcpy (nbytes, ret, sizeof (nbytes));
    free (ret);
}

这是将值从一个线程传输到另一个线程的常见模式。发送线程分配内存、复制值并传递指针。接收线程获取指针，复制出值并释放指针。