base64加密解密详解程序员

    #include "StdAfx.h" 
    #include "base64.h"   
    #include <iostream>   
       
    static const std::string base64_chars =    
                 "ABCDEFGHIJKLMNOPQRSTUVWXYZ"   
                 "abcdefghijklmnopqrstuvwxyz"   
                 "0123456789+/"; 
       
       
    static inline bool is_base64(unsigned char c) {   
      return (isalnum(c) || (c == '+') || (c == '/'));   
    }   
       
    std::string base64_encode(unsigned char const* bytes_to_encode, unsigned int in_len) {   
      std::string ret;   
      int i = 0;   
      int j = 0;   
      unsigned char char_array_3[3];   
      unsigned char char_array_4[4];   
       
      while (in_len--) {   
        char_array_3[i++] = *(bytes_to_encode++);   
        if (i == 3) {   
          char_array_4[0] = (char_array_3[0] & 0xfc) >> 2;   
          char_array_4[1] = ((char_array_3[0] & 0x03) << 4) + ((char_array_3[1] & 0xf0) >> 4);   
          char_array_4[2] = ((char_array_3[1] & 0x0f) << 2) + ((char_array_3[2] & 0xc0) >> 6);   
          char_array_4[3] = char_array_3[2] & 0x3f;   
       
          for(i = 0; (i <4) ; i++)   
            ret += base64_chars[char_array_4[i]];   
          i = 0;   
        }   
      }   
       
      if (i)   
      {   
        for(j = i; j < 3; j++)   
          char_array_3[j] = '/0';   
       
        char_array_4[0] = (char_array_3[0] & 0xfc) >> 2;   
        char_array_4[1] = ((char_array_3[0] & 0x03) << 4) + ((char_array_3[1] & 0xf0) >> 4);   
        char_array_4[2] = ((char_array_3[1] & 0x0f) << 2) + ((char_array_3[2] & 0xc0) >> 6);   
        char_array_4[3] = char_array_3[2] & 0x3f;   
       
        for (j = 0; (j < i + 1); j++)   
          ret += base64_chars[char_array_4[j]];   
       
        while((i++ < 3))   
          ret += '=';   
       
      }   
       
      return ret;   
       
    }   
       
    std::string base64_decode(std::string const& encoded_string) {   
      int in_len = encoded_string.size();   
      int i = 0;   
      int j = 0;   
      int in_ = 0;   
      unsigned char char_array_4[4], char_array_3[3];   
      std::string ret;   
       
      while (in_len-- && ( encoded_string[in_] != '=') && is_base64(encoded_string[in_])) {   
        char_array_4[i++] = encoded_string[in_]; in_++;   
        if (i ==4) {   
          for (i = 0; i <4; i++)   
            char_array_4[i] = base64_chars.find(char_array_4[i]);   
       
          char_array_3[0] = (char_array_4[0] << 2) + ((char_array_4[1] & 0x30) >> 4);   
          char_array_3[1] = ((char_array_4[1] & 0xf) << 4) + ((char_array_4[2] & 0x3c) >> 2);   
          char_array_3[2] = ((char_array_4[2] & 0x3) << 6) + char_array_4[3];   
       
          for (i = 0; (i < 3); i++)   
            ret += char_array_3[i];   
          i = 0;   
        }   
      }   
       
      if (i) {   
        for (j = i; j <4; j++)   
          char_array_4[j] = 0;   
       
        for (j = 0; j <4; j++)   
          char_array_4[j] = base64_chars.find(char_array_4[j]);   
       
        char_array_3[0] = (char_array_4[0] << 2) + ((char_array_4[1] & 0x30) >> 4);   
        char_array_3[1] = ((char_array_4[1] & 0xf) << 4) + ((char_array_4[2] & 0x3c) >> 2);   
        char_array_3[2] = ((char_array_4[2] & 0x3) << 6) + char_array_4[3];   
       
        for (j = 0; (j < i - 1); j++) ret += char_array_3[j];   
      }   
       
      return ret;   
    }