How to change a text file's name in C++?

Question

I would like to change a txt file's name, but I can not find how to do this.

For example, I want to rename foo.txt to boo.txt in my C++ program.

Answer 1

C++17's <filesystem> Updates!

Years after now we have <filesystem> in C++ standard. Therefore, the complaint mentioned in the other post and comments "C++ does not directly support file systems" is no longer valid!

The compiler which supports ISO c++17 or later, now we can use std::filesystem::rename and do as follows:

#include <filesystem>  // std::filesystem::rename
#include <string_view> // std::string_view
using namespace std::literals;

int main()
{
    const std::filesystem::path path{ "D:/...complete directory" };
    std::filesystem::rename(path / "foo.txt"sv, path / "bar.txt"sv);
}

---

What if we need to rename a group of files in a directory under some conditions or for a specific extension. Let's wrap the logic into a class, then.

#include <filesystem>  // std::filesystem::rename
#include <regex>       // std::regex_replace
#include <iostream>
#include <string>
using namespace std::string_literals;
namespace fs = std::filesystem;

class FileRenamer /* final */
{
private:
    const fs::path mPath;
    const fs::path mExtension;

private:
    template<typename LogicFunc>
    bool renameImpli(const LogicFunc& func, const fs::path& extension = {}) noexcept
    {
        bool result = true;
        const fs::path extToCheck = extension.empty() ? this->mExtension : extension;

        // iterate through all the files in the given directory
        for (const auto& dirEntry : fs::directory_iterator(mPath))
        {
            if (fs::is_regular_file(dirEntry)  && dirEntry.path().extension() == extToCheck)
            {
                const std::string currentFileName = dirEntry.path().filename().string();
                const std::string newFileName = std::invoke(func, currentFileName);
                try
                {
                    fs::rename(mPath / currentFileName, mPath / newFileName);
                }
                catch (fs::filesystem_error& error) // if the renaming was unsuccessful
                {
                    std::cout << error.code() << "\n" << error.what() << "\n";
                    result = false; // at least one of the renaming was unsuccessful!
                }
            }
        }
        return result;
    }

public:
    explicit FileRenamer(fs::path path, fs::path extension = { ".txt" }) noexcept
        : mPath{ std::move(path) }
        , mExtension{ std::move(extension) }
    {}
    // other constructors as per!

    bool findAndReplace(const std::string& findWhat, const std::string& replaceWith, const fs::path& extension = {})
    {
        const auto logic = [&](const std::string& currentFileName) noexcept {
            return std::regex_replace(currentFileName, std::regex{ findWhat }, replaceWith);
        };
        return renameImpli(logic, extension);
    }

    bool renameAll(const std::string& fileName, fs::path extension = {})
    {
        auto index{ 1u };
        const auto logic = [&](const std::string&) noexcept { 
            return std::to_string(index++) + " - "s + fileName + extension.string(); 
        };
        return renameImpli(logic, extension);
    }
};

int main()
{
    FileRenamer fileRenamer{  "D:/"}; // ...complete directory

    /*! Rename the files in the given directory with specific extension (.txt by default)
     * in such a way that, filename contained the passed string (i.e. here "foo") will be
     * replaced to what mentioned (i.e. here "bar").
     * Ex:    foo.txt           -->  bar.txt
     *        pre_foo_post.txt  -->  File of bar.txt
     *        File of foo.txt   -->  pre_bar_post.txt
     */
    fileRenamer.findAndReplace("foo"s, "bar"s);

    /*! All the files in the given directory with specific extension (.txt by default)
     * will be replaced to specific filename provided, additional with an index.
     * Ex:    foo.txt           -->  1 - foo.txt
     *        pre_foo_post.txt  -->  2 - foo.txt
     *        File of foo.txt   -->  3 - foo.txt
     */
    fileRenamer.renameAll("foo", ".txt");
}

Answer 2

Filesystem support is notably absent from the C++ standard library. As Jerry Coffin's answer shows, there actually is a rename function in stdio (contrary to the popular belief which I shared). There are however many filesystem-related appliances that the standard lib does not cover, hence the existence of Boost::Filesystem (notably manipulating directories and retrieving information about files).

This is a design decision to make C++ less constrained (i.e. make it possible to compile on a wide range of platforms including embedded systems where the idea of a file is non-existent).

To perform file operations, one has two options:

• Use the API of the target OS

• Use a library that provides a unified interface across platforms

Boost::Filesystem is such C++ library that abstracts away platform differences.

You can use the Boost::Filesystem::rename to rename a file.

Answer 3

#include <stdio.h> (or <cstdio>) and use rename (or std::rename):

rename("oldname.txt", "newname.txt");

Contrary to popular belief, this is included in the standard library, and is portable up to a point -- though of course the allowable contents of the strings will vary with the target system.