Question

我创建了一个线程，它应该返回一个发送给它的sqrt整数，它在返回int值时工作正常，但是当我想返回double或float值时，它会返回一些疯狂的数字，如何改变它？

以下是可行的代码：

int* function(int* x) {

printf("My argument: %d \n", *x);
int *y = malloc(sizeof(int));
*y=sqrt(*x);
return y;
}

int main(int argc, char* argv[])
{
pthread_t thread;
int arg = 123;
int *retVal;


pthread_create(&thread, NULL, (void * ( * ) (void *))function, &arg);

pthread_join(thread, (void **) &retVal);
printf("Sqrt of our argument: %d\n", * retVal);
free(retVal);
return 0;

}

但是当我把它变成：

double* function(int* x) {


double *y = malloc(sizeof(double));
*y=sqrt(*x);
printf("My argument: %d \n", *x);
return y;
}

int main(int argc, char* argv[])
{
pthread_t thread;
int arg = 123;
double *retVal;


pthread_create(&thread, NULL, (void * ( * ) (void *))function, &arg);

pthread_join(thread, (void **) &retVal);
printf("Sqrt of our argument: %d\n", * retVal);
free(retVal);
return 0;
}

它返回1076244058

Answer 1

你的改变是错误的

printf("Sqrt of our argument: %d\n", * retVal);

必须是

printf("Sqrt of our argument: %f\n", * retVal);

我猜您的编译器会告诉您类似

的内容

warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘double *’ [-Wformat=]

BTW你的实现会调用未定义的行为转换函数：看看this SO answer

如前所述，您可以使用arg将值传回main，而不是从任务函数返回。

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

void* function(void* x)
{
    double *y = x;

    *y = sqrt(*y);

    return x;
}

int main(void)
{
    pthread_t thread;
    double arg = 123;
    void *retVal = NULL;

    pthread_create(&thread, NULL, function, &arg);

    pthread_join(thread, &retVal);
    printf("Sqrt of our argument using arg   : %f\n", arg);

    if (retVal != NULL)
    {
        printf("Sqrt of our argument using retVal: %f\n", *((double *)retVal));
    }

    return 0;
}

C / Threads，返回值

1 个答案: