This repository is more or less archived.
If you need support or customization for existing projects, it is still available (please contact info at ifcquery.com)
For new projects, I recommend Web-ifc (https://github.com/ThatOpen/engine_web-ifc), since it fulfills the same purpose, CSG operations are more stable, and it can run also in WASM.

IfcSplitAndMerge is a light weight but high performance application based on web-ifc (not IFC++): https://github.com/ifcquery/IfcSplitAndMerge

The IFC library used in IfcSplitAndMerge is called web-ifc https://github.com/ThatOpen/engine_web-ifc. It does not have an object oriented approach for all IFC entities like IFC++. Instead it has a tape reader, so the STEP file content is kept as-is, just with tokens inserted before each attribute, which allows positioning the read cursor to read all entities and attributes with a very low memory footprint and high performance.

Web-ifc is so light weight, it can be directly compiled into a C++ console or GUI application, or linked as a library on Windows or Linux. It even compiles and runs efficiently as WebAssembly.

https://github.com/ifcquery/IfcFileLoader is an example C++ project that demonstrates how to load an IFC file, read elements, create meshes etc. using web-ifc. It does not convert the meshes into OSG geometry and has no Qt based UI like IfcSplitAndMerge.