C++简单实现Base64的编解码

Base64是个很简单的将数据编码为可见字符的算法。就是将原始数据每6个位取出来，找一个可见字符代替，这样4个可见字符刚好可以代替原来的3个字节，原理不多说，直接上代码。

PS:代码只实现对可见字符的加解密，不可打印的还要修改。

#include <string>
using namespace std;

string Code("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/");

string Base64Encode(string data)
{
   size_t len = data.size() / 3;
   string out;
   const unsigned char* input = (unsigned char*)data.data();

   for (size_t i = 0; i < len; i++){
       out += Code[input[0] >> 2];
       out += Code[((input[0] & 0x03) << 4 )+ (input[1] >> 4)];
       out += Code[((input[1] & 0x0f) << 2) + (input[2] >> 6)];
       out += Code[input[2] & 0x3f];
       input += 3;
   }

   len = data.size();
   if (len % 3 == 1) {
       out += Code[input[0] >> 2];
       out += Code[(input[0] & 0x03) << 4];
       out += "==";
   }
   else if (len % 3 == 2) {
       out += Code[input[0] >> 2];

       out += Code[((input[0] & 0x03) << 4) + (input[1] >> 4)];
       out += Code[(input[1] & 0x0f) << 2];
       out += "=";
   }

   return out;
}

unsigned char GetBaseValue(char data)
{
   if (data > 'a' - 1) {
       return data - 'a' + 26;
   }
   else if (data > 'A' - 1) {
       return data - 'A';
   }
   else if (data > '0' - 1) {
       return data - '0' + 52;
   }
   else if (data == '+') {
       return 62;
   }
   else if (data == '/') {
       return 63;
   }
   return 0;
}

string Base64Decode(string data)
{
   string out;
   unsigned char value[4];
   size_t len = data.size() / 4 - 1;
   const unsigned char* input = (unsigned char*)data.data();
   for (size_t i = 0; i < len; i++) {
       value[0] = GetBaseValue(input[0]);
       value[1] = GetBaseValue(input[1]);
       value[2] = GetBaseValue(input[2]);
       value[3] = GetBaseValue(input[3]);
       input += 4;

       out.push_back((value[0] << 2) + (value[1] >> 4));
       out.push_back((value[1] << 4) + (value[2] >> 2));
       out.push_back((value[2] << 6) + value[3]);
   }
   value[0] = GetBaseValue(input[0]);
   value[1] = GetBaseValue(input[1]);
   out.push_back((value[0] << 2) + (value[1] >> 4));
   if (input[2] != '=') {
       value[2] = GetBaseValue(input[2]);
       out.push_back((value[1] << 4) + (value[2] >> 2));
   }
   if (input[3] != '=') {
       value[3] = GetBaseValue(input[3]);
       out.push_back((value[2] << 6) + value[3]);
   }

return out;
}

来源：CSDN

作者：Heworld_guo

链接：https://blog.csdn.net/qq_24977505/article/details/103783465

标签

input

base64

data

unsigned