C源代码实现Base64编码与解码示例

// Base64.cpp : 定义控制台应用程序的入口点。
#include <stdio.h>
#include <stdlib.h>
#include <iostream>

#include <string>
//转换前 aaaaaabb ccccdddd eeffffff
//转换后 00aaaaaa 00bbcccc 00ddddee 00ffffff 

unsigned char EncodeIndex[] = {
'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P',
'Q','R','S','T','U','V','W','X','Y','Z','a','b','c','d','e','f',
'g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v',
'w','x','y','z','0','1','2','3','4','5','6','7','8','9','+','/'};
unsigned char DecodeIndex[] = {
0x40,0x40,0x40,0x40,0x40,0x40,0x40,0x40,0x40,0x40,0x40,0x40,0x40,0x40,0x40,0x40,
0x40,0x40,0x40,0x40,0x40,0x40,0x40,0x40,0x40,0x40,0x40,0x3E,0x40,0x40,0x40,0x3F,
0x40,0x40,0x40,0x40,0x40,0x40,0x40,0x40,0x40,0x40,0x40,0x40,0x40,0x40,0x40,0x40,
0x34,0x35,0x36,0x37,0x38,0x39,0x3A,0x3B,0x3C,0x3D,0x40,0x40,0x40,0x40,0x40,0x40,
0x40,0x00,0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0x09,0x0A,0x0B,0x0C,0x0D,0x0E,
0x0F,0x10,0x11,0x12,0x13,0x14,0x15,0x16,0x17,0x18,0x19,0x40,0x40,0x40,0x40,0x40,
0x40,0x1A,0x1B,0x1C,0x1D,0x1E,0x1F,0x20,0x21,0x22,0x23,0x24,0x25,0x26,0x27,0x28,
0x29,0x2A,0x2B,0x2C,0x2D,0x2E,0x2F,0x30,0x31,0x32,0x33,0x40,0x40,0x40,0x40,0x40};
void Base64_Encode(unsigned char* src,unsigned char* dest, int srclen)
{
int sign = 0;
for (int i = 0; i!= srclen; i++,src++,dest++)
{
switch(sign)
{

case 0:
*(dest) = EncodeIndex[*src >> 2];
break;
case 1:
*dest = EncodeIndex[((*(src-1)  & 0x03) << 4) | (((*src) & 0xF0) >> 4)];
break;
case 2:
*dest = EncodeIndex[((*(src-1) &0x0F) << 2) | ((*(src) & 0xC0) >> 6)];
*(++dest) = EncodeIndex[(*(src) &0x3F)];
break;
}
(sign == 2)?(sign = 0):(sign++);
}
switch(sign)
{
case 0:
break;
case 1:
*(dest++) = EncodeIndex[((*(src-1)  & 0x03) << 4) | (((*src) & 0xF0) >> 4)];
*(dest++) = '=';
*(dest++) = '=';
break;
case 2:
*(dest++) = EncodeIndex[((*(src-1) &0x0F) << 2) | ((*(src) & 0xC0) >> 6)];
*(dest++) = '=';
break;
default:
break;
}
}