BOOL ValidateHostName(
	LPCTSTR lpszHostName,
	LPTSTR lpszAddress,
	INT nMaxLength
);

BOOL ValidateHostName(
	LPCTSTR lpszHostName,
	CString& strAddress
);

The ValidateHostName method determines if the specified host name is valid and returns its IP address.

Parameters

lpszHostName

A null-terminated string which specifies the host name. The method will fail If this parameter is NULL or an empty string.

lpszAddress

A null-terminated string buffer which will contain the IP address of the host. If specified, this string must be large enough to store the complete IP address, including the terminating null character. If this parameter is NULL or the nMaxLength parameter is zero, it will be ignored and the IP address will not be returned. An alternate version of this method accepts a reference to a CString object if MFC or ATL is used with the project.

nMaxLength

An integer value that specifies the maximum number of characters which can be copied into the lpszAddress string buffer. The buffer must be large enough to store the complete address. Because this method can return either an IPv4 or IPv6 address, it is recommended the minimum length for the buffer to be 46 characters. If this parameter is zero, the lpszAddress parameter will be ignored.

Return Value

If the method succeeds, the host name is valid and the return value will be non-zero. If the method fails, the host name could not be resolved to an IP address and the return value will be zero. To get extended error information, call the GetLastError method.

Remarks

The ValidateHostName method provides a convenient way to determine if a host name is valid by attempting to resolve the name into an IP address. It is similar to calling the NormalizeHostName method to obtain the canonical form of the host name, calling GetAddress to obtain the IP address and then calling FormatAddress to return the string representation of the host's IP address.

If the Unicode version of this method is used, any non-ASCII characters in the host name will be automatically encoded into a compatible format and then resolved to an IP address. If you are unsure if an internationalized domain name will be specified as the host name, it is recommended you use the Unicode version.

The lpszHostName parameter can only specify a host name or IP address and cannot be a URL. If you want your application to support providing a URL in addition to a host name, use the GetUrlHostName method to extract the host name from the URL. You can then provide the host name to this method to obtain its IP address.

If the lpszHostName parameter specifies a valid IPv4 or IPv6 address string instead of a host name, this method will return a copy of that IP address in the buffer provided by the caller. This allows the method to be used in cases where a user may input either a host name or IP address. To determine if the IP address has a corresponding host name, use the GetHostName method.

Requirements

Minimum Desktop Platform: Windows 7 Service Pack 1
Minimum Server Platform: Windows Server 2008 R2 Service Pack 1
Header File: cswsock11.h
Import Library: cswskv11.lib
Unicode: Implemented as Unicode and ANSI versions

See Also

FormatAddress, GetAddress, GetHostAddress, GetHostName, GetUrlHostName, NormalizeHostName

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