C语言 Connect：非socket上的socket操作
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Connect: Socket operation on non-socket
提问by Nmzzz
I'm new to unix network programming and I have tried to write a program to connect to Google's server. However, I got a error while using the connect() function. (OS: OS X)
我是 unix 网络编程的新手，我尝试编写一个程序来连接到 Google 的服务器。但是，在使用 connect() 函数时出现错误。（操作系统：OS X）
Connect error: Socket operation on non-socket
连接错误：非套接字上的套接字操作
I have worked at it for 4 hours but I could not find out the problem. Here is my code:
我已经工作了 4 个小时，但我找不到问题所在。这是我的代码：
#define SERVPORT 80
int main (int argc, char **argv)
{
int i, sockfd;
struct hostent *host;
struct sockaddr_in serv_addr;
if ( (host = gethostbyname(argv[1])) == NULL) {
printf("gethostbyname error\n");
exit(1);
}
for (i = 0; host->h_addr_list[i]; i++) {
if ( (sockfd = socket(AF_INET, SOCK_STREAM, 0) == -1)) {
printf("socket error\n");
exit(1);
}
bzero(&serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons(SERVPORT);
serv_addr.sin_addr = *( (struct in_addr *)host->h_addr_list[i]);
const char *ip = inet_ntoa(serv_addr.sin_addr);
printf("connect to %s\n", ip);
if (connect(sockfd, (struct sockaddr *) &serv_addr,
sizeof(struct sockaddr)) == -1) {
printf("connect error:%s\n", strerror(errno));
exit(1);
}
}
return 0;
}
回答by selbie
I see the problem. It's this line:
我看到了问题。这是这一行：
if ( (sockfd = socket(AF_INET, SOCK_STREAM, 0) == -1))
The == operator has precedence over the = operator. Look at the way you have the parentheses structured on that expression a bit more carefully to see what I mean. sockfd is getting initialize to "0" as a result of being assigned a boolean expression (socket(...) == -1).
== 运算符优先于 = 运算符。仔细看看你在那个表达式上构造括号的方式，看看我的意思。由于被分配了一个布尔表达式 (socket(...) == -1)，sockfd 被初始化为“0”。
Change the socket initialization to this:
将套接字初始化更改为：
for (i = 0; host->h_addr_list[i]; i++)
{
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd == -1)
{
printf("socket error\n");
exit(1);
}
Or if you prefer the "assign and compare" on the same line approach, you can probably say this:
或者，如果您更喜欢同一行方法中的“分配和比较”，您可以这样说：
if ( (sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1)
Notice the subtle difference.
注意细微的差别。
