How to get file extension from string in C++

Question

Given a string "filename.conf", how to I verify the extension part?

I need a cross platform solution.

Answer 1

With C++17 and its std::filesystem::path::extension (the library is the successor to boost::filesystem) you would make your statement more expressive than using e.g. std::string.

#include <iostream>
#include <filesystem> // C++17
namespace fs = std::filesystem;

int main()
{
    fs::path filePath = "my/path/to/myFile.conf";
    if (filePath.extension() == ".conf") // Heed the dot.
    {
        std::cout << filePath.stem() << " is a valid type.";
        // Output: "myFile is a valid type."
    }
    else
    {
        std::cout << filePath.filename() << " is an invalid type.";
        // Output: "myFile.cfg is an invalid type"
    }
}

See also std::filesystem::path::stem, std::filesystem::path::filename.