fmt

A very small, simple, and fast formatting library for C++.

Usage

std::map<std::string, int> map{ {"key1", 10}, {"key2", 20}};

std::string str = fmt::format("string {} number {} bool {} null {} map {}", "hello", 10, true, nullptr, map);

std::cout << str;

// or print it directly

fmt::println("string {} number {} bool {} null {} map {}", "hello", 10, true, nullptr, map)

// output: string hello number 10 bool true null null map [ key1: 10, key2: 20 ]

Functions

all functions are under the fmt namespace

• print prints to stdout using printf
• println as expected does the same but prints with a new line. uses puts.
• fatal prints and exits with status code -1
• to_string converts the given type to a string
• string_of determines the best way to get the string of a types and returns its string value
• format the base function for doing formatting

Overload example

you can overload the fmt::to_string function to make it work with other types.

struct User
{
    int id;
    std::string name;
};

namespace fmt
{
    std::string to_string(const User& user)
    {
        return std::to_string(user.id) + ": " + user.name;
    }
}

#include "fmt.hpp"

int main()
{

    User user{10, "john"};
    std::string str = fmt::format("user -> {}", user);

    std::cout << str;
}

the header must be included after the overload so the string_of function can have access to the overload. alternatively you can just put it directly in the fmt.hpp file

Motivation

I created this library because I didn't want to depend on a large library to do basic formatting, I just wanted the most simple formatting in a tiny hpp file. In terms of performance it's much faster than sprintf. on my machine with an average input sprintf would take anywhere from 6k ns to 10k ns, but fmt::format would take 400 to 500 ns.