sm::base64

Base64 encoding and decoding

import sm.base64;

Module file: sm/base64.cppm. This module is adapted, with thanks, from a base64 snippet by mvorbrodt.

Table of Contents

• Summary
• Decoding errors

Summary

sm::base64::encode and sm::base64::decode convert between raw bytes (std::vector<std::uint8_t>) and base64-encoded text (std::string), using the standard alphabet (A–Z, a–z, 0–9, +, /) and = padding.

std::vector<std::uint8_t> data = { 'H', 'e', 'l', 'l', 'o' };
std::string encoded = sm::base64::encode (data);
// encoded == "SGVsbG8="

std::vector<std::uint8_t> decoded = sm::base64::decode (encoded);
// decoded == data

Binary (non-text) data round-trips just as well:

std::vector<std::uint8_t> bytes = { 0xDE, 0xAD, 0xBE, 0xEF };
std::string encoded = sm::base64::encode (bytes); // "3q2+7w=="

Decoding errors

decode throws std::runtime_error in three cases:

• the input’s length isn’t a multiple of 4 ("Invalid base64 length!");
• the input contains a character outside the base64 alphabet and padding character ("Invalid character in base64!");
• a = padding character appears somewhere other than in a valid position at the end of the input ("Invalid padding in base64!").

try {
    sm::base64::decode ("abc"); // length 3, not a multiple of 4
} catch (const std::exception& e) {
    std::cout << "caught: " << e.what() << std::endl; // "caught: Invalid base64 length!"
}

This page was authored with AI, based on human written code in base64.cppm. Checked by Seb James