Check if a specific TCP or UDP port is open

• Download CheckOpenPorts.zip-14.38KB

Introduction

This article will show you how to scan in c++ a TCP or UDP port to see if it’s open.

The TCP (Transmission Control Protocol ) is intended to provide a reliable process-to-process communication service in a multinetwork environment.  The TCP is intended to be a host-to-host protocol in common use in multiple networks.

User Datagram Protocol (UDP) is one of the core protocols of the Internet Protocol Suite. Using UDP, programs on networked computers can send short messages sometimes known as datagrams (using Datagram Sockets) to one another.

UDP does not guarantee reliability or ordering in the way that TCP does. Datagrams may arrive out of order, appear duplicated, or go missing without notice. Avoiding the overhead of checking whether every packet actually arrived makes UDP faster and more efficient, for applications that do not need guaranteed delivery.

How to use this code

To use this code you should include windows.h and to link the Wsock32 library as follows: 

#include <windows.h> #pragma comment(lib,"Wsock32.lib")

1. Check TCP Port

BOOL CheckPortTCP(short int dwPort , char*ipAddressStr) { struct sockaddr_in client; int sock; client.sin_family = AF_INET; client.sin_port = htons(dwPort); client.sin_addr.s_addr = inet_addr(ipAddressStr); sock = (int) socket(AF_INET, SOCK_STREAM, 0); return (connect(sock, (struct sockaddr *) &client,sizeof(client)) == 0); }

2. Check UDP Port

BOOL CheckPortUDP(short int dwPort , char *ipAddressStr) { struct sockaddr_in client; int sock; client.sin_family = AF_INET; client.sin_port = htons(dwPort); client.sin_addr.s_addr = inet_addr(ipAddressStr); sock = (int) socket(AF_INET, SOCK_DGRAM, 0); return (bind(sock, (SOCKADDR FAR *) &client,sizeof(SOCKADDR_IN)) == SOCKET_ERROR); }

Before using any socket functions call WSAStartup. The WSAStartup function must be the first Windows Sockets function called by an application or DLL. It allows an application or DLL to specify the version of Windows Sockets required and to retrieve details of the specific Windows Sockets implementation. The application or DLL can only issue further Windows Sockets functions after a successfully calling WSAStartup.

You can call WSAStartup as follow:

int _tmain(int argc, _TCHAR* argv[]) { WSADATA wsaData; if(WSAStartup(0x0101, &wsaData) == 0) { if(CheckPortTCP(80,"127.0.0.1")) printf("Port 80 open\n"); else printf("Port 80 not open\n"); if(CheckPortUDP(5001 ,"127.0.0.1")) printf("Port 5001 open\n"); else printf("Port 5001 not open\n"); } WSACleanup(); return 0; }

License

This article, along with any associated source code and files, is licensed under The Intelliproject Open License (IPOL)

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