base64案例分享

喜欢ヅ旅行 2024-04-18 08:39 49阅读 0赞

Base64是一种用64个字符来表示任意二进制数据的方法。

Base64编码可用于在HTTP环境下传递较长的标识信息以及二进制数据（例如图片文件、PDF文件等等）。

Base64的原理很简单，首先，准备一个包含64个字符的码表：

\[‘A’, ‘B’, ‘C’, … ‘a’, ‘b’, ‘c’, … ‘0’, ‘1’, … ‘+’, ‘/’\]  
也就是52个大小写字母加上10个阿拉伯数字再加上两个字符‘+’、‘/’。字符索引为0~63。  
然后，对二进制数据进行处理，每3个字节划为一组，一共是3x8=24bit，再将24bit划为4组，每组正好6个bit（可表示2的6次方、即64个数）：  
![在这里插入图片描述][20190904100142280.png]

这样我们就得到了4个数字，将其作为索引查码表，获得相应的4个字符，就是编码后的字符串。

所以，Base64编码会把3字节的二进制数据编码为4字节的文本数据，长度增加33%。

如果要编码的二进制数据不是3的倍数，最后会剩下1个或2个字节怎么办？Base64用\\x00字节在末尾补足后，再在编码的末尾加上1个或2个=号，表示补了多少字节，解码的时候，会自动去掉。  
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版权声明：本文为CSDN博主「zhangzeyuaaa」的原创文章，遵循 CC 4.0 BY-SA 版权协议，转载请附上原文出处链接及本声明。  
原文链接：https://blog.csdn.net/zhangzeyuaaa/article/details/49949587

#include <string>
    
    std::string base64_encode(unsigned char const* , unsigned int len);
    std::string base64_decode(std::string const& s);

/* 
       base64.cpp and base64.h
    
       Copyright (C) 2004-2008 René Nyffenegger
    
       This source code is provided 'as-is', without any express or implied
       warranty. In no event will the author be held liable for any damages
       arising from the use of this software.
    
       Permission is granted to anyone to use this software for any purpose,
       including commercial applications, and to alter it and redistribute it
       freely, subject to the following restrictions:
    
       1. The origin of this source code must not be misrepresented; you must not
          claim that you wrote the original source code. If you use this source code
          in a product, an acknowledgment in the product documentation would be
          appreciated but is not required.
    
       2. Altered source versions must be plainly marked as such, and must not be
          misrepresented as being the original source code.
    
       3. This notice may not be removed or altered from any source distribution.
    
       René Nyffenegger rene.nyffenegger@adp-gmbh.ch
    
    */
    #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) {
      size_t 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;
    }

[20190904100142280.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/17/09dcda9398fe49cdae57a2eeee1962d2.png