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std::filesy...::extension(3)  C++ Standard Libary std::filesy...::extension(3)

NAME
       std::filesystem::path::extension	- std::filesystem::path::extension

Synopsis
	  path extension() const;  (since C++17)

	  Returns  the extension of the	filename component of the generic-for-
       mat view	of *this.

	  If the filename() component of the generic-format  path  contains  a
       period (.), and is
	  not  one of the special filesystem elements dot or dot-dot, then the
       extension is the
	  substring beginning at the rightmost period (including  the  period)
       and until the end
	  of the pathname.

	  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 pathname is either . or .., or	if filename() does not contain
       the '.'
	  character, then empty	path is	returned.

	  Additional behavior may be defined by	the implementations  for  file
       systems which
	  append additional elements (such as alternate	data streams or	parti-
       tioned dataset
	  names) to extensions.

Parameters
	  (none)

Return value
	  The extension	of the current pathname	or an empty path if there's no
       extension.

Exceptions
	  May throw implementation-defined exceptions.

Notes
	  The extension	as returned by this function includes a	period to make
       it possible to
	  distinguish  the file	that ends with a period	(function returns ".")
       from a file with
	  no extension (function returns "").

	  On a non-POSIX system, it is possible	that p.stem()+p.extension() !=
       p.filename()
	  even though generic-format versions are the same.

Example
       // Run this code

	#include <iostream>
	#include <filesystem>
	namespace fs = std::filesystem;

	int main()
	{
	    std::cout << fs::path("/foo/bar.txt").extension() << '\n'
		      << fs::path("/foo/bar.").extension() << '\n'
		      << fs::path("/foo/bar").extension() << '\n'
		      << fs::path("/foo/bar.txt/bar.cc").extension() <<	'\n'
		      << fs::path("/foo/bar.txt/bar.").extension() << '\n'
		      << fs::path("/foo/bar.txt/bar").extension() << '\n'
		      << fs::path("/foo/.").extension()	<< '\n'
		      << fs::path("/foo/..").extension() << '\n'
		      << fs::path("/foo/.hidden").extension() << '\n'
		      << fs::path("/foo/..bar").extension() << '\n';
	}

Output:
	".txt"
	"."
	""
	".cc"
	"."
	""
	""
	""
	""
	".bar"

See also
	  filename	    returns the	filename path component
			    (public member function)
			    returns the	stem path component (filename  without
       the final
	  stem		    extension)
			    (public member function)
	  replace_extension replaces the extension
			    (public member function)
	  has_extension	     checks  if	 the corresponding path	element	is not
       empty
			    (public member function)

http://cppreference.com		  2022.07.31	  std::filesy...::extension(3)

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