学步园

Base64是网络上最常见的用于传输8Bit字节代码的编码方式之一，大家可以查看RFC2045～RFC2049，

上面有MIME的详细规范。Base64编码可用于在HTTP环境下传递较长的标识信息。例如，在Java Persistence系统Hibernate中，

就采用了Base64来将一个较长的唯一标识符（一般为128-bit的UUID）编码为一个字符串，用作HTTP表单和HTTP
GET URL中的参数。

在其他应用程序中，也常常需要把二进制数据编码为适合放在URL（包括隐藏表单域）中的形式。此时，采用Base64编码不仅比较简短，

同时也具有不可读性，即所编码的数据不会被人用肉眼所直接看。

转化表

代码示例

void encode(TCHAR *src, int src_len, TCHAR *dst)

{

        int i = 0, j = 0;

char base64_map[65] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

        for (; i < src_len - src_len % 3; i += 3) {

                dst[j++] = base64_map[(src[i] >> 2) & 0x3F];

                dst[j++] = base64_map[((src[i] << 4) & 0x30) + ((src[i + 1] >> 4) & 0xF)];

                dst[j++] = base64_map[((src[i + 1] << 2) & 0x3C) + ((src[i + 2] >> 6) & 0x3)];

                dst[j++] = base64_map[src[i + 2] & 0x3F];

        }

 

        if (src_len % 3 == 1) {

                 dst[j++] = base64_map[(src[i] >> 2) & 0x3F];

                 dst[j++] = base64_map[(src[i] << 4) & 0x30];

                 dst[j++] = '=';

                 dst[j++] = '=';

        }

        else if (src_len % 3 == 2) {

                dst[j++] = base64_map[(src[i] >> 2) & 0x3F];

                dst[j++] = base64_map[((src[i] << 4) & 0x30) + ((src[i + 1] >> 4) & 0xF)];

                dst[j++] = base64_map[(src[i + 1] << 2) & 0x3C];

                dst[j++] = '=';

        }

 

        dst[j] = '\0';

}

 

void decode(TCHAR *src, int src_len, char *dst)

{

        int i = 0, j = 0;

        unsigned char base64_decode_map[256] = {

             255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,

          /*20*/255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,

          /*40*/255, 255, 255, 62, 255, 255, 255, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 255, 255,

             255, 0, 255, 255, 255, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,

             15, 16, 17, 18, 19, 20, 21/*V*/, 22/*W*/, 23/*X*/, 24/*Y*/, 25/*Z*/, 255, 255, 255, 255, 255, 255, 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, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,

             255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,

             255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,

             255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,

             255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,

             255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,

             255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255};

 

        for (; i < src_len; i += 4) {

                dst[j++] = base64_decode_map[src[i]] << 2 |

                        base64_decode_map[src[i + 1]] >> 4;

                dst[j++] = base64_decode_map[src[i + 1]] << 4 |

                        base64_decode_map[src[i + 2]] >> 2;

                dst[j++] = base64_decode_map[src[i + 2]] << 6 |

                        base64_decode_map[src[i + 3]];

        }

 

   //     dst[j] = '\0';
 dst[j] = '\0';
}