Parse IP addresses


Application Security Testing: An Integral Part of DevOps

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Very often, if you write Internet applications, you need to verify IP address user entered and make sure that it's correct. So lets see how we can do that without a lot of troubles.
First of all we need to add declarations of the following function to header file of the dialog.

#include <winsock.h>

void WINAPI DDX_IPAddress(CDataExchange* pDX, int nIDC, UINT & value);
To implement data exchange you need to call DDX_IPAddress function from within your dialog DoDataExchange function
Now add following code to the implementation file of the dialog, and do not forget to include ws2_32.lib into the project or you'll get a lot of linking errors.
// DDX routine fo IP address translation
void WINAPI DDX_IPAddress(CDataExchange* pDX, int nIDC, UINT & value)
	// from dialog to class ?
	if( pDX->m_bSaveAndValidate)
		CString Val;
		BOOL bValid = true;


		for( int i = 0; i < Val.GetLength(); i++)
			// let's check if all entered char in entered
			// IP address are digits
			if(Val[i] == '.')

			if(isdigit(Val[i]) == 0)
				bValid = false;

			value = inet_addr(Val);
			if(value == INADDR_NONE)
				pDX->m_pDlgWnd->MessageBox("The entered IP address is invalid.");
			pDX->m_pDlgWnd->MessageBox("IP address can only have digits and dots.");
		// if the value is a valid IP address store it in the child control
		in_addr IPaddress;
		memcpy(&IPaddress, &value, 4);
		CString Address = inet_ntoa(IPaddress);

Last updated: 14 May 1998


  • Quicker way? Try this..

    Posted by Legacy on 04/06/1999 12:00am

    Originally posted by: Chris Morse Sebrell

    The sscanf() function works well too:

    // Assign Address at some point..
    CString Address = "";

    // Parse Address
    int IP[4];
    if(sscanf((LPCTSTR) Address, "%d.%d.%d.%d", &IP[0], &IP[1], &IP[2], &IP[3]) == 4)
    // Now IP[0] = 20, IP[1] = 15, IP[2] = 7, IP[3] = 4...
    SendUpdateMessageUDP(IP, "Programming Is Great!");

    // CHRIS!

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