Base64

#include<string>
#ifndef BASE_64_H
#define BASE_64_H
class Base64
{
private:
    std::string  _base64_table;
    static const char base64_pad = '=';
public:
    Base64() {
        _base64_table= "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"; /*这是Base64编码使用的标准字典*/
    }
    std::string Encode(const unsigned char* str, int bytes);
    std::string Decode(const char* str, int bytes);
    void Debug(bool open = true);

};
#endif

#include <iostream>
#include<string>
#include<cstring>
#include "base_64.h"
using namespace std;
std::string Base64::Encode(const unsigned char* str, int bytes)
{
    int num = 0, bin = 0, i;
    std::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;
}
std::string Base64::Decode(const char* str, int length) {
    //解码表
    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;
    std::string _decode_result;
    const char* current = str;
    char ch;
    while ((ch = *current++) != '\0' && length-- > 0)
    {
        if (ch == base64_pad) { // 当前一个字符是“=”号
            /*
            先说明一个概念：在解码时，4个字符为一组进行一轮字符匹配。
            两个条件：
                1、如果某一轮匹配的第二个是“=”且第三个字符不是“=”，说明这个带解析字符串不合法，直接返回空
                2、如果当前“=”不是第二个字符，且后面的字符只包含空白符，则说明这个这个条件合法，可以继续。
            */
            if (*current != '=' && (i % 4) == 1) {
                return NULL;
            }
            continue;
        }
        ch = DecodeTable[ch];
        //这个很重要，用来过滤所有不合法的字符
        if (ch < 0) { /* a space or some other separator character, we simply skip over */
            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()
{
    Base64 base64;
    unsigned char str[] = "Hello World!";
    string en_str = base64.Encode(str, strlen((char*)str));
    string de_str = base64.Decode(en_str.c_str(), strlen(en_str.c_str()));
    std::cout <<str<< endl;
    std::cout << en_str << endl;
    std::cout << de_str << endl;
}