c - 为什么我会收到这些警告？

Question

编译器针对以下代码段显示以下警告。请帮我改正。

if((tmp_n = (struct dot *)shmat(shm_net, NULL, 0)) == (int *) -1) { }
warning: comparison of distinct pointer types lacks a cast [enabled by default]

它是一个 C 程序，该代码段用于将共享内存段附加到指针 **tmp_n，其类型为 struct dot。

结构点 {int weight; int tmv;};

Answer 1

试试这个

if((tmp_n = (struct dot *)shmat(shm_net, NULL, 0)) == (void *) -1) { }

并查看 man-page ，它指出:

Return Value
On success shmat() returns the address of the attached shared memory segment; 
on error (void *) -1 is returned, and errno is set to indicate the cause of the error.