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

NAME
     std::filesystem::path::replace_extension	 -    std::filesystem::path::re-
     place_extension

Synopsis
	path& replace_extension( const path& replacement  =  path()  );   (since
     C++17)

	Replaces  the  extension with replacement or removes it when the default
     value of
	replacement is used.

	Firstly, if this path  has  an	extension(),  it  is  removed  from  the
     generic-format view
	of the pathname.

	Then,  a  dot  character  is  appended to the generic-format view of the
     pathname, if
	replacement is not empty and does not begin with a dot character.

	Then replacement is appended as if by operator+=(replacement).

Parameters
	replacement - the extension to replace with

Return value
	*this

Exceptions
	May throw implementation-defined exceptions.

Notes
	The type of replacement is std::filesystem::path even though it  is  not
     intended to
	represent an object on the file system in order to correctly account for
     the
	filesystem character encoding.

Example
     // Run this code

      #include <filesystem>
      #include <iomanip>
      #include <iostream>
      #include <utility>

      int main()
      {
	  const int width1{18}, width2{11}; // columns' width

	  std::cout << std::left << std::setw(width1) << "Path:"
		    << std::setw(width2) << "Ext:" << "Result:\n";
	  for (const auto& [p, e] : {
		  std::make_pair("/foo/bar.jpg", ".png"),
		  {"/foo/bar.jpg", "png"},
		  {"/foo/bar.jpg", "."},
		  {"/foo/bar.jpg", ""},
		  {"/foo/bar.", "png"},
		  {"/foo/bar", ".png"},
		  {"/foo/bar", "png"},
		  {"/foo/bar", "."},
		  {"/foo/bar", ""},
		  {"/foo/.", ".png"},
		  {"/foo/.", "png"},
		  {"/foo/.", "."},
		  {"/foo/.", ""},
		  {"/foo/", ".png"},
		  {"/foo/", "png"}})
	  {
	      std::filesystem::path path{p}, ext{e};
	      std::cout  <<  std::setw(width1)	<<  path << std::setw(width2) <<
     ext;
	      path.replace_extension(ext);
	      std::cout << path << '\n';
	  }
      }

Output:
      Path:		Ext:	   Result:
      "/foo/bar.jpg"	".png"	   "/foo/bar.png"
      "/foo/bar.jpg"	"png"	   "/foo/bar.png"
      "/foo/bar.jpg"	"."	   "/foo/bar."
      "/foo/bar.jpg"	""	   "/foo/bar"
      "/foo/bar."	"png"	   "/foo/bar.png"
      "/foo/bar"	".png"	   "/foo/bar.png"
      "/foo/bar"	"png"	   "/foo/bar.png"
      "/foo/bar"	"."	   "/foo/bar."
      "/foo/bar"	""	   "/foo/bar"
      "/foo/."		".png"	   "/foo/..png"
      "/foo/."		"png"	   "/foo/..png"
      "/foo/."		"."	   "/foo/.."
      "/foo/."		""	   "/foo/."
      "/foo/"		".png"	   "/foo/.png"
      "/foo/"		"png"	   "/foo/.png"

See also
	extension     returns the file extension path component
		      (public member function)
	filename      returns the filename path component
		      (public member function)
	stem	      returns the stem path component (filename without the  fi-
     nal extension)
		      (public member function)
	has_extension checks if the corresponding path element is not empty
		      (public member function)

http://cppreference.com 	   2024.06.10	    std::filesy...e_extension(3)
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