// Code written by Li Zexuan (Looks handsome)
// This code is written by DataErr0r and plagiarism is prohibited!!!
#include <bits/stdc++.h>
#ifndef BASE_64_H
#define BASE_64_H
using namespace std;

class Base64 {
	private:
		std::string _base64_table;
		static const char base64_pad = '=';
	public:
		Base64() {
			_base64_table = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"; 
		}
		std::string Encode(const unsigned char * str, int bytes);
		std::string Decode(const char *str, int bytes);
		void Debug(bool open = true);
};
#endif

string Base64::Encode(const unsigned char * str, int bytes) {
	int num = 0, bin = 0, i;
	string _encode_result;
	const unsigned char * current;
	current = str;
	while (bytes > 2) {
		_encode_result += _base64_table[current[0] >> 2];
		_encode_result += _base64_table[((current[0] & 0x03) << 4) + (current[1] >> 4)];
		_encode_result += _base64_table[((current[1] & 0x0f) << 2) + (current[2] >> 6)];
		_encode_result += _base64_table[current[2] & 0x3f];

		current += 3;
		bytes -= 3;
	}
	if (bytes > 0) {
		_encode_result += _base64_table[current[0] >> 2];
		if (bytes % 3 == 1) {
			_encode_result += _base64_table[(current[0] & 0x03) << 4];
			_encode_result += "==";
		} else if (bytes % 3 == 2) {
			_encode_result += _base64_table[((current[0] & 0x03) << 4) + (current[1] >> 4)];
			_encode_result += _base64_table[(current[1] & 0x0f) << 2];
			_encode_result += "=";
		}
	}
	return _encode_result;
}

string Base64::Decode(const char *str, int length) {
	const char DecodeTable[] = {
		-2, -2, -2, -2, -2, -2, -2, -2, -2, -1, -1, -2, -2, -1, -2, -2,
		    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,
		    -1, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, 62, -2, -2, -2, 63,
		    52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -2, -2, -2, -2, -2, -2,
		    -2,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,
		    15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -2, -2, -2, -2, -2,
		    -2, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
		    41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -2, -2, -2, -2, -2,
		    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,
		    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,
		    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,
		    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,
		    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,
		    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,
		    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,
		    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2
	    };
	int bin = 0, i = 0, pos = 0;
	string _decode_result;
	const char *current = str;
	char ch;
		while ( (ch = *current++) != '\0' && length-- > 0 ) {
		if (ch == base64_pad) {
			if (*current != '=' && (i % 4) == 1) {
				return NULL;
			}
			continue;
		}
		ch = DecodeTable[ch];
		if (ch < 0 ) { 
			continue;
		}
		switch (i % 4) {
		case 0:
			bin = ch << 2;
			break;
		case 1:
			bin |= ch >> 4;
			_decode_result += bin;
			bin = ( ch & 0x0f ) << 4;
			break;
		case 2:
			bin |= ch >> 2;
			_decode_result += bin;
			bin = ( ch & 0x03 ) << 6;
			break;
		case 3:
			bin |= ch;
			_decode_result += bin;
			break;
		}
		i++;
	}
	return _decode_result;
}


int main() {
	string str;
	getline(cin, str);
	int n = str.length();
	str += '0';
	unsigned char uch[1000000];
	strcpy((char *)uch, str.c_str());
	strncpy((char *)uch, str.c_str(), str.length());
	memcpy(uch, str.c_str(), str.length());
	snprintf((char *)uch, str.length(), str.c_str());
	string normal, encoded;
	int len = sizeof(str) - 1;
	Base64 *base = new Base64();
	encoded = base->Encode(uch, len);
	cout << "编码后为：" << encoded << endl;
    len = encoded.length();
	const char * uch2 = encoded.c_str();
	normal = base->Decode(uch2, len);
	cout << "解码后为：" << normal << endl;
	return 0;
}

四周前：改加密条将unsigned char str[] = "你知道吗，这个Base64很不好写的qwq";改成你要加密的改你知道吗，这个Base64很不好写的qwq部分

2023/6/11 17:45 @ 我已经可以自己输入了！！！