Question

我正在学习Pthreads。我的代码按照我想要的方式执行，我可以使用它。但是它给了我关于编译的警告。

我使用编译：

gcc test.c -o test -pthread

与GCC 4.8.1。我收到了警告

test.c: In function ‘main’:
test.c:39:46: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
     pthread_create(&(tid[i]), &attr, runner, (void *) i);
                                              ^
test.c: In function ‘runner’:
test.c:54:22: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
   int threadnumber = (int) param;
                      ^

以下代码出现此错误：

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

#define MAX_THREADS 10

int sum; /* this data is shared by the thread(s) */
void *runner(void * param);

int main(int argc, char *argv[])
{
  int num_threads, i;
  pthread_t tid[MAX_THREADS];     /* the thread identifiers  */
  pthread_attr_t attr; /* set of thread attributes */

  if (argc != 2) {
    fprintf(stderr, "usage:  test <integer value>\n");
    exit(EXIT_FAILURE);
  }

  if (atoi(argv[1]) <= 0) {
    fprintf(stderr,"%d must be > 0\n", atoi(argv[1]));
    exit(EXIT_FAILURE);
  }

  if (atoi(argv[1]) > MAX_THREADS) {
    fprintf(stderr,"%d must be <= %d\n", atoi(argv[1]), MAX_THREADS);
    exit(EXIT_FAILURE);
  }

  num_threads = atoi(argv[1]);
  printf("The number of threads is %d\n", num_threads);

  /* get the default attributes */
  pthread_attr_init(&attr);

  /* create the threads */
  for (i=0; i<num_threads; i++) {
    pthread_create(&(tid[i]), &attr, runner, (void *) i);
    printf("Creating thread number %d, tid=%lu \n", i, tid[i]);
  }

  /* now wait for the threads to exit */
  for (i=0; i<num_threads; i++) {
    pthread_join(tid[i],NULL);
  }
  return 0;
}

/* The thread will begin control in this function */
void *runner(void * param)
{
  int i;
  int threadnumber = (int) param;
  for (i=0; i<1000; i++) printf("Thread number=%d, i=%d\n", threadnumber, i);
  pthread_exit(0);
}

如何修复此警告？

Answer 1

快速修复可能只会转发long而不是int。在许多系统上，sizeof(long) == sizeof(void *)。

更好的想法可能是使用intptr_t。

int threadnumber = (intptr_t) param;

和

pthread_create(&(tid[i]), &attr, runner, (void *)(intptr_t)i);

Answer 2

pthread_create(&(tid[i]), &attr, runner, (void *) i);

您正在传递本地变量 i作为runner，sizeof(void*) == 8和sizeof(int) == 4（64位）的参数。

如果要传递i，则应将其包装为指针或其他内容：

void *runner(void * param) {
  int id = *((int*)param);
  delete param;
}

int tid = new int; *tid = i;
pthread_create(&(tid[i]), &attr, runner, tid);

您可能只想要i，在这种情况下，以下内容应该是安全的（但远非推荐）：

void *runner(void * param) {
  int id = (int)param;
}

pthread_create(&(tid[i]), &attr, runner, (void*)(unsigned long long)(i));

Answer 3

我也得到了同样的警告。所以为了解决我的警告我将int转换为long然后这个警告就消失了。关于警告“从不同大小的整数转换为指针”，您可以保留此警告，因为指针可以保存任何变量的值，因为64x中的指针是64位而32x中的指针是32位。

Answer 4

尝试传递

#Code block A

import os
for i in dir(os):
    print (help(os.i))

警告：从/向不同大小的整数转换为/从指针转换

4 个答案: