std::filesystem::path::stem (3) - Linux Manuals
path stem() const; (since C++17)
Returns the filename identified by the generic-format path stripped of its extension.
Returns the substring from the beginning of filename() up to and not including the last period (.) character, with the following exceptions:
If the first character in the filename is a period, that period is ignored (a filename like ".profile" is not treated as an extension)
If the filename is one of the special filesystem components dot or dot-dot, or if it has no periods, the function returns the entire filename().
The stem of the filename identified by the path (i.e. the filename without the final extension).
// Run this code
filename (public member function)
extension (public member function)