WinHTTP Constants

WinHTTP uses the following constants:

Error Messages

Error messages specific to the WinHTTP functions. These functions also return Windows error messages where appropriate. The value that corresponds to each constant is the value of the constant for the application programming interface (API) functions and the lower 16 bits of the error number for the WinHttpRequest object.

HTTP Status Codes

Constants and corresponding values that indicate HTTP status codes returned by servers on the Internet.

Option Flags

Option flags supported by WinHttpQueryOption and WinHttpSetOption. All valid option flags have a value greater than or equal to WINHTTP_FIRST_OPTION and less than or equal to WINHTTP_LAST_OPTION.


A WORD value indicating the port.


Internet schemes supported by WinHTTP.

Query Info Flags

Attributes and modifiers used by WinHttpQueryHeaders.