为什么getservbyname没有返回正确的端口号？

Question

在我的C:\ Windows\System32\drivers\etc\service文件中,我看到了

echo 7/tcp echo 7/udp

所以我写了一个程序来测试getservbyname

#include <stdio.h>
#include <winsock2.h>
#include <iostream>
#pragma comment(lib,"ws2_32.lib")  // winsock library

using namespace std;

int main(int argc, char *argv[]) 
{
WSADATA wsa;
SOCKET s;
sockaddr_in server;
servent     *serverInfo;


cout << "Initializing Winsock...." << endl;

if (WSAStartup(MAKEWORD(2,2), &wsa) != 0) {
    cout << "Failed. Error code: " << WSAGetLastError();
    return 1;
}
cout << "initialized." << endl; 

serverInfo = getservbyname("echo", "tcp");
cout << "service echo:: s_name is " << serverInfo->s_name << endl; 
cout << "service echo:: s_aliases is " << serverInfo->s_aliases << endl; 
cout << "service echo:: s_port is " << serverInfo->s_port << endl; 
cout << "service echo:: s_proto is " << serverInfo->s_proto << endl; 

return 0;
}

当我运行它时,下面是显示的结果:

Initializing Winsock....
initialized.
service echo:: s_name is echo
service echo:: s_aliases is 00724F08
service echo:: s_port is 1792
service echo:: s_proto is tcp

我的问题是为什么s_port是1792而不是7？我在文件服务中找不到1792.有人可以解释一下吗？非常感谢.

Answer 1

7*256 = 1792

它是网络字节顺序.尝试打印ntohs(serverInfo-> s_port).

如果你打算使用它来构建一个,sockaddr_in你可以直接将它复制到sin_port那个网络字节顺序.