The actual name format is implementation defined. Here's the output from clang 17: int main():9 auto main()::(anonymous class)::operator()(std::source_

The actual name format is implementation defined. Here's the output from clang 17: int main():9 auto main()::(anonymous class)::operator()(std::source_location) const:5 so your formatter/helper would need to be compiler-aware, although to extract “main” in both cases I suppose you can just grab everything between the first whitespace and (, although I assume both types would contain specifiers like const where included in the return type. I don’t know what MSVC outputs.