在CentOS6.2 64位下编译一下代码，不通过，提示
./11_2.cpp: In function ‘int main(int, char**)’:
./11_2.cpp:28: 错误：从‘void*’到‘int’的转换损失精度
./11_2.cpp:31: 错误：从‘void*’到‘int’的转换损失精度
1 #include <unistd.h> 2 #include <cstdio> 3 #include <pthread.h> 4 5 using namespace std; 6 7 void *thr_fn1(void *arg) 8 { 9 printf("thread 1 returning "); 10 return (void*)1; 11 } 12 13 void *thr_fn2(void *arg) 14 { 15 printf("thread 2 exiting "); 16 pthread_exit((void*)2); 17 } 18 19 int main(int argc, char **argv) 20 { 21 pthread_t tid1, tid2; 22 void *tret; 23 24 pthread_create(&tid1, NULL, thr_fn1, NULL); 25 pthread_create(&tid2, NULL, thr_fn2, NULL); 26 27 pthread_join(tid1, &tret); 28 printf("thread 1 exit code %ld ", (long)tret); 29 30 pthread_join(tid2, &tret); 31 printf("thread 2 exit code %ld ", (long)tret); 32 33 return 0; 34 }
既然提示精度损失，那么看一下各自的精度即可：
1 #include <iostream> 2 3 using namespace std; 4 5 int main(int argc, char **argv) 6 { 7 cout << sizeof(int) << endl; 8 cout << sizeof(long) << endl; 9 cout << sizeof(void*) << endl; 10 11 return 0; 12 }
执行结果：
4
8
8
好吧，确实是精度损失了，从4个字节转换为8个字节。但是问题来了，为什么在64位下，指针是8个字节呢？