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

#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"