1、base64编码的作用：
base64编码的东西，任何人都可以解码，所以称之为加密和解密是不合适的，其作用是：便于数据再网络上的传输。举个简单的例子，你使用SMTP协议 （Simple Mail Transfer Protocol 简单邮件传输协议）来发送邮件，因为这个协议是基于文本的协议，所以，如果邮件中包含一幅图片，我们知道图片的存储格式是二进制数据（binary data）而非文本格式，我们必须将二进制的数据编码成文本格式，这时候Base 64 Encoding就派上用场了。
2、C++实现的base64编码类及其使用方法：
1）、类：
#include "stdafx.h" #include#include #include #include #include using namespace std; namespace { static char encoding_table[] = {'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', '+', '/' }; static char *decoding_table = NULL; static int mod_table[] = { 0, 2, 1 }; void build_decoding_table() { decoding_table = (char*)malloc(256); for (int i = 0; i < 64; i++) decoding_table[(unsigned char)encoding_table[i]] = i; } char* base64_encode(const unsigned char *data, size_t input_length, size_t *output_length) { *output_length = 4 * ((input_length + 2) / 3); char *encoded_data = (char*)malloc(*output_length + 1); if (encoded_data == NULL) return NULL; memset(encoded_data, 0, *output_length + 1); for (int i = 0, j = 0; i < input_length;) { uint32_t octet_a = i < input_length ? (unsigned char)data[i++] : 0; uint32_t octet_b = i < input_length ? (unsigned char)data[i++] : 0; uint32_t octet_c = i < input_length ? (unsigned char)data[i++] : 0; uint32_t triple = (octet_a << 0x10) + (octet_b << 0x08) + octet_c; encoded_data[j++] = encoding_table[(triple >> 3 * 6) & 0x3F]; encoded_data[j++] = encoding_table[(triple >> 2 * 6) & 0x3F]; encoded_data[j++] = encoding_table[(triple >> 1 * 6) & 0x3F]; encoded_data[j++] = encoding_table[(triple >> 0 * 6) & 0x3F]; } for (int i = 0; i < mod_table[input_length % 3]; i++) encoded_data[*output_length - 1 - i] = '='; return encoded_data; } unsigned char* base64_decode(const char *data, size_t input_length, size_t *output_length) { if (decoding_table == NULL) build_decoding_table(); if (input_length % 4 != 0) return NULL; *output_length = input_length / 4 * 3; if (data[input_length - 1] == '=') (*output_length)--; if (data[input_length - 2] == '=') (*output_length)--; unsigned char *decoded_data = (unsigned char*)malloc(*output_length); if (decoded_data == NULL) return NULL; memset(decoded_data, 0, *output_length); for (int i = 0, j = 0; i < input_length;) { uint32_t sextet_a = data[i] == '=' ? 0 & i++ : decoding_table[data[i++]]; uint32_t sextet_b = data[i] == '=' ? 0 & i++ : decoding_table[data[i++]]; uint32_t sextet_c = data[i] == '=' ? 0 & i++ : decoding_table[data[i++]]; uint32_t sextet_d = data[i] == '=' ? 0 & i++ : decoding_table[data[i++]]; uint32_t triple = (sextet_a << 3 * 6) + (sextet_b << 2 * 6) + (sextet_c << 1 * 6) + (sextet_d << 0 * 6); if (j < *output_length) decoded_data[j++] = (triple >> 2 * 8) & 0xFF; if (j < *output_length) decoded_data[j++] = (triple >> 1 * 8) & 0xFF; if (j < *output_length) decoded_data[j++] = (triple >> 0 * 8) & 0xFF; } return decoded_data; } void base64_cleanup() { free(decoding_table); } } // namespace
2）、使用注意：
特别要注意的是：在编码前，我们应该将编码内容转换成通用的UTF8格式，解码出来的内容也要转换成自己的编码格式来显示，比如：unicode/ansi等格式。否则的话，对于中文内容，如果和其他语言进行中文内容的传输操作，比如java，它解码出来的内容会是乱码。
3）、编码转换函数，由于我本地是ANSI编码格式，所以下面给出ANSI与UTF8编码格式的相互转换函数，如果你本地使用的是UNICODE编码格式，就要用到UNICODE与UTF8之间的相互转换：
std::string ANSItoUTF8(const char * ansi)
{
int len = MultiByteToWideChar(CP_ACP, 0, ansi, -1, NULL, 0);
wchar_t* wstr = new wchar_t[len+1];
memset(wstr, 0, len+1);
MultiByteToWideChar(CP_ACP, 0, ansi, -1, wstr, len);
len = WideCharToMultiByte(CP_UTF8, 0, wstr, -1, NULL, 0, NULL, NULL);
char* str = new char[len+1];
memset(str, 0, len+1);
WideCharToMultiByte(CP_UTF8, 0, wstr, -1, str, len, NULL, NULL);
if(wstr) delete[] wstr;
std::string ret = str;
if(str) delete[] str;
return ret;
}
std::string UTF8toANSI(const char* utf8)
{
int len = MultiByteToWideChar(CP_UTF8, 0, utf8, -1, NULL, 0);
wchar_t* wstr = new wchar_t[len+1];
memset(wstr, 0, len+1);
MultiByteToWideChar(CP_UTF8, 0, utf8, -1, wstr, len);
len = WideCharToMultiByte(CP_ACP, 0, wstr, -1, NULL, 0, NULL, NULL);
char* str = new char[len+1];
memset(str, 0, len+1);
WideCharToMultiByte(CP_ACP, 0, wstr, -1, str, len, NULL, NULL);
if(wstr) delete[] wstr;
std::string ret = str;
if(str) delete[] str;
return ret;
}
4）、实例：
// base64Test.cpp : 定义控制台应用程序的入口点? // #include "stdafx.h" #include#include #include #include #include using namespace std; namespace { static char encoding_table[] = {'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', '+', '/' }; static char *decoding_table = NULL; static int mod_table[] = { 0, 2, 1 }; void build_decoding_table() { decoding_table = (char*)malloc(256); for (int i = 0; i < 64; i++) decoding_table[(unsigned char)encoding_table[i]] = i; } char* base64_encode(const unsigned char *data, size_t input_length, size_t *output_length) { *output_length = 4 * ((input_length + 2) / 3); char *encoded_data = (char*)malloc(*output_length); if (encoded_data == NULL) return NULL; for (int i = 0, j = 0; i < input_length;) { uint32_t octet_a = i < input_length ? (unsigned char)data[i++] : 0; uint32_t octet_b = i < input_length ? (unsigned char)data[i++] : 0; uint32_t octet_c = i < input_length ? (unsigned char)data[i++] : 0; uint32_t triple = (octet_a << 0x10) + (octet_b << 0x08) + octet_c; encoded_data[j++] = encoding_table[(triple >> 3 * 6) & 0x3F]; encoded_data[j++] = encoding_table[(triple >> 2 * 6) & 0x3F]; encoded_data[j++] = encoding_table[(triple >> 1 * 6) & 0x3F]; encoded_data[j++] = encoding_table[(triple >> 0 * 6) & 0x3F]; } for (int i = 0; i < mod_table[input_length % 3]; i++) encoded_data[*output_length - 1 - i] = '='; return encoded_data; } unsigned char* base64_decode(const char *data, size_t input_length, size_t *output_length) { if (decoding_table == NULL) build_decoding_table(); if (input_length % 4 != 0) return NULL; *output_length = input_length / 4 * 3; if (data[input_length - 1] == '=') (*output_length)--; if (data[input_length - 2] == '=') (*output_length)--; unsigned char *decoded_data = (unsigned char*)malloc(*output_length); if (decoded_data == NULL) return NULL; for (int i = 0, j = 0; i < input_length;) { uint32_t sextet_a = data[i] == '=' ? 0 & i++ : decoding_table[data[i++]]; uint32_t sextet_b = data[i] == '=' ? 0 & i++ : decoding_table[data[i++]]; uint32_t sextet_c = data[i] == '=' ? 0 & i++ : decoding_table[data[i++]]; uint32_t sextet_d = data[i] == '=' ? 0 & i++ : decoding_table[data[i++]]; uint32_t triple = (sextet_a << 3 * 6) + (sextet_b << 2 * 6) + (sextet_c << 1 * 6) + (sextet_d << 0 * 6); if (j < *output_length) decoded_data[j++] = (triple >> 2 * 8) & 0xFF; if (j < *output_length) decoded_data[j++] = (triple >> 1 * 8) & 0xFF; if (j < *output_length) decoded_data[j++] = (triple >> 0 * 8) & 0xFF; } return decoded_data; } void base64_cleanup() { free(decoding_table); } } // namespace std::string ANSItoUTF8(const char * ansi) { int len = MultiByteToWideChar(CP_ACP, 0, ansi, -1, NULL, 0); wchar_t* wstr = new wchar_t[len+1]; memset(wstr, 0, len+1); MultiByteToWideChar(CP_ACP, 0, ansi, -1, wstr, len); len = WideCharToMultiByte(CP_UTF8, 0, wstr, -1, NULL, 0, NULL, NULL); char* str = new char[len+1]; memset(str, 0, len+1); WideCharToMultiByte(CP_UTF8, 0, wstr, -1, str, len, NULL, NULL); if(wstr) delete[] wstr; std::string ret = str; if(str) delete[] str; return ret; } std::string UTF8toANSI(const char* utf8) { int len = MultiByteToWideChar(CP_UTF8, 0, utf8, -1, NULL, 0); wchar_t* wstr = new wchar_t[len+1]; memset(wstr, 0, len+1); MultiByteToWideChar(CP_UTF8, 0, utf8, -1, wstr, len); len = WideCharToMultiByte(CP_ACP, 0, wstr, -1, NULL, 0, NULL, NULL); char* str = new char[len+1]; memset(str, 0, len+1); WideCharToMultiByte(CP_ACP, 0, wstr, -1, str, len, NULL, NULL); if(wstr) delete[] wstr; std::string ret = str; if(str) delete[] str; return ret; } int _tmain(int argc, _TCHAR* argv[]) { std::string strSrc = "我热爱C++语言"; string strUtf8 = ANSItoUTF8(strSrc.c_str()); fprintf(stdout, "str: %sn", strSrc.c_str()); size_t output_length_encode = 0; char* strEncode = base64_encode((const unsigned char*)strUtf8.c_str(), strUtf8.length(), &output_length_encode); //打印编码结果 std::string tmpEncode(strEncode, output_length_encode); fprintf(stdout, "encode result: %sn", tmpEncode.c_str()); size_t output_length_decode = 0; unsigned char* strDecode= base64_decode(strEncode, output_length_encode, &output_length_decode); std::string tmpDecode((char*)strDecode, output_length_decode); //打印解密结果 string strDecodeUtf8 = UTF8toANSI(tmpDecode.c_str()); fprintf(stdout, "str decode2: %sn", strDecodeUtf8.c_str()); free(strEncode); free(strDecode); base64_cleanup(); system("pause"); return 0; }
结果：
与在线的base64编码对照结果：
