base64实现

最近在复习，把写的base64发在这里

#include<iostream>
#include<String>
#include<cstdlib>
#include <vector>


std::string en(std::string str) {
	using namespace std;
	const string table = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
	std::vector<uint8_t> input;
	std::vector<uint8_t> output;
	//初始化input
	for (char c : str) {
		input.push_back(c);
	}

	//长度检查
	const uint8_t len_before = str.length();
	uint8_t fix_num = 0;
	switch (len_before % 3) {
	case 1:
		fix_num++;
	case 2:
		fix_num++;
	}
	for (int i = 0; i < fix_num; i++) {
		input.push_back('\0');
	}
	//执行编码
	uint8_t save[4] = {};

	for (int i = 0; i < len_before; i += 3) {
		save[0] = input[i] >> 2;
		output.push_back(table[save[0]]);
		save[1] = (input[i] & 0b00000011) << 4 | input[i + 1] >> 4;
		output.push_back(table[save[1]]);
		save[2] = (input[i + 1] & 0b00001111) << 2 | input[i + 2] >> 6;
		save[3] = input[i + 2] & 0b00111111;
		output.push_back(table[save[2]]);
		output.push_back(table[save[3]]);
	}
	//处理末尾数据
	if (output.back() == table[0])
	{
		for (int i = 0; i < fix_num; i++) {
			output.pop_back();
		}
		for (int i = 0; i < fix_num; i++) {
			output.push_back(table[64]);
		}
	}
	//组合字符串并返回
	string res(output.begin(), output.end());
	return res;
}


std::string de(std::string str) {
	using namespace std;
	const string table = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
	vector<uint8_t> input;
	vector<uint8_t> output;
	// 初始化input
	for (char c : str) {
		input.push_back(table.find(c));
	}
	// 执行解码
	for (int i = 0; i < input.size(); i += 4) {
		output.push_back((input[i] << 2) | (input[i + 1] >> 4));
		if (input[i + 2] != 64) {
			output.push_back((input[i + 1] << 4) | (input[i + 2] >> 2));
		}
		if (input[i + 3] != 64) {
			output.push_back((input[i + 2] << 6) | input[i + 3]);
		}
	}
	// 组合字符串并返回
	string res(output.begin(), output.end());
	return res;
}




int main(void) {
	using namespace std;
	cout << "please use Ctrl+Z to quit\n";
	cout << "please input your string:\n";

	string str;
	while (getline(cin, str))
	{
		cout << en(str) << endl << de(en(str)) << endl;
		cout << "\nplease input your string:\n";
	}
	return 0;

}