What is the right way to add secondary extension to boost::filesystem::path?

Question

I want to append additional extension to a path:

namespace fs = boost::filesystem;
fs::path append_extension(const fs::path& path, const fs::path& ext);

Expected behavior:

• append_extension("foo.txt", ".log") -> "foo.txt.log"
• append_extension("foo.txt", "log") -> "foo.txt.log"
• append_extension("foo", "log") -> "foo.log"

Is it possible to implement append_extension without string manipulations with dot character?

Answer 1

How about

namespace fs = boost::filesystem;
fs::path append_extension(const fs::path& path, const fs::path& ext) {
    auto sz_ext = ext.c_str();
    if ('.' == *sz_ext) ++sz_ext;
    return path.string<std::string>() + "." + sz_ext;
}

Is it possible to implement append_extension without string manipulations with dot character?

No. Extensions aren't a thing, they're merely conventions. Secondary extensions aren't even a convention, so you're on your own.

DEMO

Live On Coliru

#include <boost/filesystem.hpp>
#include <boost/property_tree/string_path.hpp>

namespace fs = boost::filesystem;
fs::path append_extension(const fs::path& path, const fs::path& ext) {
    auto sz_ext = ext.c_str();
    if ('.' == *sz_ext) ++sz_ext;
    return path.string<std::string>() + "." + sz_ext;
}
#include <iostream>

int main() {
    std::cout << append_extension("foo.txt", ".log") << "\n"; // -> "foo.txt.log"
    std::cout << append_extension("foo.txt", "log") << "\n"; // -> "foo.txt.log"
    std::cout << append_extension("foo", "log") << "\n"; // -> "foo.log"
}

Prints

"foo.txt.log"
"foo.txt.log"
"foo.log"