XLL Connector is a modern C++ library that makes existing functions available for use in Excel spreadsheets. All you need to do is to add one line for each function you want to export to Excel. A minimal working example is as simple as follows:

#include "XllAddin.h"

std::wstring ReverseString(const std::wstring &s)
{
	return std::wstring(s.crbegin(), s.crend());
}

EXPORT_XLL_FUNCTION(ReverseString);

BOOL WINAPI DllMain(HANDLE hInstance, ULONG fdwReason, LPVOID lpReserved)
{
	return TRUE;
}

The following assumes you have already built a DLL that contains functions you want to make available for use in Excel. Follow four simple steps to make this happen:

1. Build the XLL Connector static library
2. Link the static library into your DLL
3. Mark the functions you want to export
4. Test the XLL in Excel

1. Start Visual Studio 2013 or later. This is required because XLL Connector relies on C++11 features to ensure type safety.
2. Download the source code from github. The source code contains two projects. The XllConnector project is the actual library. XllExamples.dll is a sample DLL that you can load into Excel to see it in action.
3. Build the solution XLLConnector.sln. This produces XllConnector.lib in the output directory.

The static library, XllConnector.lib, must be linked into your DLL to make it available to Excel. There are two alternatives:

• To use XllConnector as a standalone library, add it to the "Additional Dependencies" list in the DLL's linker options.
• To customize XllConnector, add the XllConnector project into your solution, and add it into the "Reference" section of the DLL project.

You don't need to export your functions or change any existing code. Just add one line (in a source file) for each function you want to expose to Excel. Suppose you have written a function Plus with the following signature:

double Plus(double, double);

To expose this function to Excel, simply add the following line:

EXPORT_XLL_FUNCTION(Plus);

This automatically generates and exports a wrapper function named XLPlus that interfaces with Excel.

You can provide more information about the UDF by the following:

EXPORT_XLL_FUNCTION(Plus)
  .Description(L"Returns the sum of two numbers.")
  .Arg(L"a", L"first number")
  .Arg(L"b", L"second number")
  .ThreadSafe();

To load the XLL into Excel automatically when you run the project, do the following:

1. Change your Debug settings to launch Excel with the XLL.
2. Hit Ctrl+F5 to run the project.
3. Excel now starts. Create a new workbook. Enter a formula that uses your UDF.

To debug the XLL, do the following:

1. Set a breakpoint in your UDF.
2. Hit F5. If Visual C++ asks you whether to proceed without loading the symbols for EXCEL.EXE, choose Yes.
3. Excel now starts. Create a new workbook. Enter a formula that uses your UDF. When the formula is evaluated, your breakpoint will be triggered and you can debug it.

Being a one-man project, there are a few limitations:

• Visual Studio 2013 or higher is required, as this library uses C++11 features such as variadic templates and move semantics.

• Only Excel 2007 and higher is supported as they expose a different interface than prior versions of Excel, which supports more parameters, longer strings, and larger worksheet range.

• Both 32-bit and 64-bit Excel are supported, but only 32-bit is tested because I don't have 64-bit Excel installed.

This project uses Apache License V2. See the LICENSE for details.