c - lpthread:编译时警告，执行时奇怪的结果

Question

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

#define NB_THREAD 2
void *func(void *arg){
        printf("thread %d \n ",(int) (int*)arg);
}
int main(int argc, char *argv[])
{
int i, status;
pthread_t tid [NB_THREAD];
        for(i=0;i<NB_THREAD; i++)
        {
                if(pthread_create(&tid[i], NULL, func, argv[i+1])!=0){
                printf("error thread create \n "); exit(1);
                }
        }
        for(i=0;i<NB_THREAD; i++)
        {
                if(pthread_join(tid[i],(void**)status)!=0){
                printf("error thread join \n"); exit(1);
                }
                else
                printf("thread success \n");
        }
        return 0;
}

gcc -std = c99 test.c -o test -lpthread

test.c: In function ‘func’:
test.c:8:25: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
  printf("thread %d \n ",(int) (int*)arg);
                         ^
test.c: In function ‘main’:
test.c:22:26: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
   if(pthread_join(tid[i],(void**)status)!=0){

有人可以向我解释吗？


>在我的终端中得到以下结果：

>螺纹-649483154
>线程0
>线程成功
>线程成功

Answer 1

您的问题似乎是func（）处理arg的方式...您将其强制转换为指向int的指针，然后将其强制转换为int ...您是否正在尝试打印出arg+1的“地址”（从main的角度来看），还是您尝试打印其值... ???

这是您的程序的稍作修改的版本，它同时打印出地址和“字符串”值...请注意，将其编译并运行如下：


  ./test你好

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

#define NB_THREAD 2
void *func(void *arg){
    printf("thread %p (-->%s<--)\n", arg, (char*)arg);
}

int main(int argc, char *argv[])
{
    int i, status;
    pthread_t tid [NB_THREAD];

    for(i=0;i<NB_THREAD; i++)
    {
        if(pthread_create(&tid[i], NULL, func, argv[i+1])!=0){
            printf("error thread create \n "); exit(1);
        }
    }
    for(i=0;i<NB_THREAD; i++)
    {
        if(pthread_join(tid[i],(void**)status)!=0){
            printf("error thread join \n"); exit(1);
        }
        else
            printf("thread sucess \n");
    }
    return 0;
}