A simple approach to convert strings from and to base64. Header only c++ library (single header).

#include <iostream>
#include "base64.hpp"
int main() {
  auto encoded_str =  base64::to_base64("Hello, World!");
  std::cout << encoded_str << std::endl; // SGVsbG8sIFdvcmxkIQ==
  auto decoded_str = base64::from_base64("SGVsbG8sIFdvcmxkIQ==");
  std::cout << decoded_str << std::endl; // Hello, World!
}

This library relies on C++17 but will exploit some C++20 features if available (e.g. bit_cast).

There are many implementations available and it may be worth looking at those. A benchmark of various c/c++ base64 implementations can be found at https://github.com/gaspardpetit/base64/ with summary results at:

• https://rawcdn.githack.com/gaspardpetit/base64/main/result/result.html (presented as base64tl)

This implementation here adopts the approach of Nick Galbreath's modp_b64 library also used by chromium (e.g. https://github.com/chromium/chromium/tree/main/third_party/modp_b64 ) but offers it as a c++ single header file. This choice was based on the good computational performance of the underpinning algorithm. We also decided to avoid relying on a c++ union to perform type punning as this, while working in practice, is strictly speaking undefined behaviour in c++: https://en.wikipedia.org/wiki/Type_punning#Use_of_union

Faster c/c++ implementations exist although these do not come as a single header library and exploit simd / openmp or similar acceleration techniques:

• https://github.com/aklomp/base64
• https://github.com/simdutf/simdutf
• https://github.com/powturbo/Turbo-Base64 (Note that this is licensed under GPL 3.0)

Many other C++ centric appraches exists although they seem to focus on readibility or genericity at the cost of performance, e.g.:

• https://github.com/matheusgomes28/base64pp (C++20 library from which we borrowed the unit test code)
• https://github.com/ReneNyffenegger/cpp-base64 (Implementation that works with older C++ versions)
• https://github.com/azawadzki/base-n (more generic baseN such as N=16 and N=32)