std::filesystem::path::replace_extension

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>
namespace fs = std::filesystem;
 
int main()
{
    std::cout << "Path:             Ext:       Result:\n" << std::left;
    for (const auto& [path, extension] : {
            std::make_pair( "/foo/bar.jpg", ".png" ),
            std::make_pair( "/foo/bar.jpg", "png"  ),
            std::make_pair( "/foo/bar.jpg", "."    ),
            std::make_pair( "/foo/bar.jpg", ""     ),
            std::make_pair( "/foo/bar."   , "png"  ),
            std::make_pair( "/foo/bar"    , ".png" ),
            std::make_pair( "/foo/bar"    , "png"  ),
            std::make_pair( "/foo/bar"    , "."    ),
            std::make_pair( "/foo/bar"    , ""     ),
            std::make_pair( "/foo/."      , ".png" ),
            std::make_pair( "/foo/."      , "png"  ),
            std::make_pair( "/foo/."      , "."    ),
            std::make_pair( "/foo/."      , ""     ),
            std::make_pair( "/foo/"       , ".png" ),
            std::make_pair( "/foo/"       , "png"  ), })
    {
        fs::path p = path, e = extension;
        std::cout << std::setw(18) << p << std::setw(11) << e;
        p.replace_extension(e);
        std::cout << p << '\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"

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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 final extension) (public member function)
has_extension	checks if the corresponding path element is not empty (public member function)