xlfRegister

int Excel12(int iFunction, 
            xloper12 *pxReturnValue, 
            int iCount, 
            xloper12 *pxDLLModuleName, 
            xloper12 *pxFunctionName, 
            xloper12 *pxTypeText, 
            xloper12 *pxWorksheetFunctionName, 
            xloper12 *pxArgumentText, 
            xloper12 *pxMacroType, 
            xloper12 *pxCategory, 
            xloper12 *pxShortcutText, 
            xloper12 *pxHelpTopic, 
            xloper12 *pxFunctionHelp, 
            xloper12 *pxArgument1, 
            xloper12 *pxArgument2, 
            ..) 

iFunction - The number corresponding to a pre-defined function or command. xlfRegister
pxReturnValue - A pointer that will hold the result
iCount - The number of arguments that are being passed in
pxDLLModuleName - The full drive, path and filename of the DLL containing the function.
pxFunctionName - The name of the function as it is exported (case sensitive)
pxTypeText - The return data type and argument data types and calling permission string.
pxWorksheetFunctionName - The name of the function to call from Excel (case sensitive)
pxArgumentText - (Optional) Argument names as a comma-delimited concatenated string. Displayed in the Function Arguments dialog box
pxMacroType - (Optional) Whether a function or command. 1 or missing = Function. 2 = Command
pxCategory - (Optional) The category in which the function is to be listed. If missing the default is User Defined
pxShortcutText - (Optional) Not used (pass xltypeNil or xltypeMissing)
pxHelpTopic - (Optional) The help topic
pxFunctionHelp - (Optional) A brief description of the function. Displayed in the Insert Function dialog box
pxArgument1 - (Optional) Argument descriptions for each argument
pxArgument2 - (Optional) Argument descriptions for each argument

Example