Search notes:

XLL

Expected exported functions

`xlAddInManagerInfo12`	Called when the Add-in Manager is invoked the first time in an Excel session in order to query information about the XLL. The pre-2007 version of this function is `xlAddInManagerInfo`,
`xlAutoAdd`	Called when the XLL is activated using the Add-in Manager (but not when Excel loads pre-installed add-ins). Used, for example, to display a dialog box, read configuration data from the registry, checking licence etc.
`xlAutoClose`	Called when the XLL is deactivated. Functions that were registered in `xlAutoOpen` don't have to be unregistered, Excel will do that when the `xlAutoClose` returns.
`xlAutoFree12`	Used to to free memory allocated on an `XLOPER12` structure. The pre-2007 version of this function is `xlAutoFree`.
`xlAutoOpen`	Used to register XLL functions and commands, initalized data strucuters etc. This function must be implemented.
`xlAutoRegister12`	Called whenever a call has been made to the XLM function `REGISTER` or the C-API equivalent `xlfRegister` (without specifying the `type_text` argument). The pre-2007 version of this function is `xlAutoRegister`.
`xlAutoRemove`	Called when the XLL is deactivated using the Add-in Manager.

Excel provides the two functions Excel12 and Excel12v to expose internal functionality to XLLs.

These functions can only be called when Excel has passed control to the XLL (but not, for example in DllMain).

Prior to Excel 2007, these functions were named Excel4 and Excel4v.

int Excel12(
      int        iFunction,
      LPXLOPER12 pxRes,
      int        iCount,
      LPXLOPER12 argument1,
                 ...
);

The value of iFunction can be one of the following constants:

`xlAbort`
`xlAsyncReturn`
`xlCoerce`
`xlDefineBinaryName`
`xlDisableXLMsgs`	Deprecated
`xlEnableXLMsgs`	Deprecated
`xlEventRegister`	Introduced in Excel 2010
`xlFree`
`xlGetBinaryName`
`xlGetHwnd`
`xlGetInst`
`xlGetName`
`xlRunningOnCluster`
`xlSet`
`xlSheetId`
`xlSheetNm`
`xlStack`
`xlUDF`
`xlfCaller`
`xlfEvaluate`
`xlfGetDef`
`xlfGetName`
`xlfRegister`	Two forms
`xlfRegisterId`
`xlfUnregister`	Two forms
`xlfSetName`
`xlcSelect`
`xlc…`	Are there other `xlc` constants?

The framework library functions makes writing XLLs easier.

These functions are found in framewrk.c (framewrk.h) and framewrk.lib.

`CallUDF`
`CancelOutstandingRequests`
`CloseSession`
`OpenSession`
`PingSession`
`ShowOptions`

Some interesting typedefs in xlcall.h.

Excel (XLL) uses wide characters for strings:

typedef WCHAR XCHAR;

Rows, columns and sheet IDs:

typedef INT32 RW;
typedef INT32 COL;
typedef DWORD_PTR IDSHEET;

XLOPER12 is a union that combines the following fields in val. How val is interpreted is defined in the member xltype (which is a DWORD).

LPXLOPER12 is pointer to XLOPER12

XLOPER12 was introduced with Excel 2007 to accomodate larger grids and to support Unicode strings.

It seems that the XLL interface allows for multithreaded programming (to be confirmed).