线程传递参数

Question

char buff[MAX_SIZE];

int main() {

    pthread_t thread[3];

    char message1 = 17;  //17 = 0x11
    char message2 = 18;
    char message3 = 19;
    char message4 = 20;

    int iret[3];
    int k;

    char message[] = {17, 18,19,20};

    /*THIS IS WORKING  

    iret[0] = pthread_create( &thread[0], NULL, write_to_buffer, (void*) &message1);
    iret[1] = pthread_create( &thread[1], NULL, write_to_buffer, (void*) &message2);
    iret[2] = pthread_create( &thread[2], NULL, write_to_buffer, (void*) &message3);
    iret[3] = pthread_create( &thread[3], NULL, write_to_buffer, (void*) &message4);
    */


    /* BUT THIS IS NOT 

    iret[0] = pthread_create( &thread[0], NULL, write_to_buffer, (void*) message);
    iret[1] = pthread_create( &thread[1], NULL, write_to_buffer, (void*) (message+1));
    iret[2] = pthread_create( &thread[2], NULL, write_to_buffer, (void*) (message+2));
    iret[3] = pthread_create( &thread[3], NULL, write_to_buffer, (void*) (message+3));

    */

    for(k=0;k<=3;k++)   {
        pthread_join( thread[k], NULL);
    }


    //rest of main

}


void *write_to_buffer( void *ptr ) {

    while(1)    {
        pthread_mutex_lock(&my_mutex);


        char *message;
        message = (char *) ptr;

        //when passing by array I'm unable to get the value in the message variable

        printf("\nMeeee = %#x  ", *(char*)ptr);



        //REST OF THE FUNCTION //logic to write to buffer

        pthread_mutex_unlock(&my_mutex);

        //SOME LOGIC I OMMITED HERE
        //to return if(indexx >= MAX_SIZE) return(NULL);        
    }   
}

我面临的问题是，当我传递数组元素时，我无法捕获线程函数中的值。但是当我传递message1、message2、message3和message4的地址时，我可以获得线程函数中传递的值

Answer 1

您的代码中有一些未定义行为的情况。您声明了大小为3的thread和iret数组，但是创建了四个线程，从而超越了这些数组的范围。这可能会影响程序的结果及其输出，因为它可能会导致您传递的数据被覆盖。