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  • ARTS-S 获取子线程返回值注意事项

    #include <stdio.h>
    #include <stdlib.h>
    #include <pthread.h>
    #include <unistd.h>
    struct foo {
        int a, b, c, d;
    };
    
    void printfoo(const char *s, const struct foo *fp)
    {
        printf("%s", s);
        printf("  structure at 0x%lx
    ", (unsigned long)fp);
        printf("  foo.a = %d
    ", fp->a);
        printf("  foo.b = %d
    ", fp->b);
        printf("  foo.c = %d
    ", fp->c);
        printf("  foo.d = %d
    ", fp->d);
    }
    
    void *thr_fn1(void *arg)
    {
        struct foo  foo = {1, 2, 3, 4};
        printfoo("thread 1:
    ", &foo);
        pthread_exit((void *)&foo);
    }
    
    void *thr_fn2(void *arg) {
        printf("thread 2: ID is %lu
    ", (unsigned long)pthread_self());
        pthread_exit((void *)0);
    }
    
    int main(void) {
        int         err;
        pthread_t   tid1, tid2;
        struct foo  *fp;
        err = pthread_create(&tid1, NULL, thr_fn1, NULL);
        if (err != 0)
            printf("can’t create thread 1:%d", err);
        err = pthread_join(tid1, (void *)&fp);
        if (err != 0)
            printf("can’t join with thread 1:%d", err);
        sleep(1);
        printf("parent starting second thread
    ");
        err = pthread_create(&tid2, NULL, thr_fn2, NULL);
        if (err != 0)
            printf("can’t create thread 2:%d", err);
        sleep(1);
        printfoo("parent:
    ", fp);
        exit(0);
    }
    // gcc -Wall main2.c -lpthread -o demo
    

    最后打印的fp的值和第一个线程中初始化的不一样。第一个线程中结构体是个局部变量,函数返回,内存被回收。所以在主线程中就不能访问fp的值。如果想在主线程中获取子线程的值,就要用malloc初始化。

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  • 原文地址:https://www.cnblogs.com/zhouyang209117/p/11148173.html
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