C++扫描指定主机开放的端口，OS提供了connect()系统调用，用于与远程主机某端口建立连接，如果远程主机该端口处于帧听状态，则connect()连接成功；否则说明该端口关闭。  

// ScanPorts.cpp : 定义控制台应用程序的入口点。
//

#include “stdafx.h”
#include
using namespace std;
#include<WinSock2.h>
#pragma comment (lib,”ws2_32.lib”)
#define STATUS_FALIED 0xFFFF
unsigned long serverIP;
long MaxThread = 200;
long ThreadCount = 0;
long *aa = &ThreadCount;

//扫描端口的线程
DWORD WINAPI ScanPort(LPVOID lpParam){
short Port = (short)lpParam;
InterlockedIncrement(aa);
//创建流式套接字
SOCKET sock = socket(AF_INET, SOCK_STREAM,0);
if (sock == INVALID_SOCKET){
cout << “创建套接字失败！” << endl;
return 0;

}
else{
    //填充服务器地址
    sockaddr_in severAddr;
    severAddr.sin\_family = AF\_INET;
    severAddr.sin_port = htons(Port);
    severAddr.sin\_addr.S\_un.S_addr = serverIP;
    //判断此机器是否打开
    connect(sock, (sockaddr*)&severAddr, sizeof(severAddr));
    struct fd_set write;
    FD_ZERO(&write);
    FD_SET(sock, &write);
    //初始化超时时间
    struct timeval timeout;
    timeout.tv_sec = 100 / 1000;
    timeout.tv_usec = 0;
    if (select(0,NULL,&write,NULL,&timeout)>0)
    {
        cout << Port <<",";
    };
    closesocket(sock);


}

InterlockedDecrement(aa);
return 0;

}

void main(int argc, char *argv[])
{
if (argc != 2){
cout << “请输入目的主机IP地址” << endl;

}
//建立与socket库的绑定
WSADATA WSAData;
if (WSAStartup(MAKEWORD(2, 2), &WSAData) != 0)
{
    cout << "WSAStartup falied!" << GetLastError() << endl;
    ExitProcess(STATUS_FALIED);
}
serverIP = inet_addr(argv\[1\]);
cout << "下列端口已开放：" << endl;
for (int i = 1; i < 1024; i++){
    //超过最大允许线程数等待
    while (ThreadCount >= MaxThread)
        Sleep(10);
    //创建线程，扫描端口
DWORD ThreadID;
CreateThread(NULL, 0, ScanPort, (LPVOID)new short(i), 0, &ThreadID);
}
//还有没有结束的线程，等待
while (ThreadCount>0)
    Sleep(50);

WSACleanup();

}