base64 c/c++实现

/**
* @brief C++ base64 编解码
* @author wid
* @date 2013-20-25
*
* @note
*/

#include <iostream>
#include <string>
#include <ctime>

const char *enkey = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

//base64 编解码函数声明
std::string b64encodestring(const std::string &strString);      //对 ASCII 字符串进行 base64 编码
std::string b64decodestring(const std::string &strString);      //对 base64 编码后的字符串进行解码

																//base64 编解码函数实现
																/**
																* @brief 对 ASCII 字符串进行 base64 编码
																*
																* @param strString 待编码的字符串
																*
																* @return srs::string 返回编码后的字符串
																*
																* @note 对于字符串中含有非 ASCII 字符串型的字符, 代码将抛出 std::string 型异常, 请捕获
																*/
std::string b64encodestring(const std::string &strString)
{
	int nByteSrc = strString.length();
	std::string pszSource = strString;

	int i = 0;
	for (i; i < nByteSrc; i++)
		if (pszSource[i] < 0 || pszSource[i] > 127)
			throw "can not encode Non-ASCII characters";

	
	std::string pszEncode(nByteSrc * 4 / 3 + 4, ‘\0‘);
	int nLoop = nByteSrc % 3 == 0 ? nByteSrc : nByteSrc - 3;
	int n = 0;
	for (i = 0; i < nLoop; i += 3)
	{
		pszEncode[n] = enkey[pszSource[i] >> 2];
		pszEncode[n + 1] = enkey[((pszSource[i] & 3) << 4) | ((pszSource[i + 1] & 0xF0) >> 4)];
		pszEncode[n + 2] = enkey[((pszSource[i + 1] & 0x0f) << 2) | ((pszSource[i + 2] & 0xc0) >> 6)];
		pszEncode[n + 3] = enkey[pszSource[i + 2] & 0x3F];
		n += 4;
	}

	switch (nByteSrc % 3)
	{
	case 0:
		pszEncode[n] = ‘\0‘;
		break;

	case 1:
		pszEncode[n] = enkey[pszSource[i] >> 2];
		pszEncode[n + 1] = enkey[((pszSource[i] & 3) << 4) | ((0 & 0xf0) >> 4)];
		pszEncode[n + 2] = ‘=‘;
		pszEncode[n + 3] = ‘=‘;
		pszEncode[n + 4] = ‘\0‘;
		break;

	case 2:
		pszEncode[n] = enkey[pszSource[i] >> 2];
		pszEncode[n + 1] = enkey[((pszSource[i] & 3) << 4) | ((pszSource[i + 1] & 0xf0) >> 4)];
		pszEncode[n + 2] = enkey[((pszSource[i + 1] & 0xf) << 2) | ((0 & 0xc0) >> 6)];
		pszEncode[n + 3] = ‘=‘;
		pszEncode[n + 4] = ‘\0‘;
		break;
	}

	return pszEncode.c_str();
}

/**
* @brief 对 base64 编码后的字符串进行解码
*
* @param strString 待解码的字符串
*
* @return std::string 返回解码后的字符串
*
* @note 对于非base64编码的字符串或已损坏的base64字符串进行解码会抛出 std::string 型异常, 请捕获
*/
std::string b64decodestring(const std::string &strString)
{
	int nByteSrc = strString.length();
	std::string pszSource = strString;

	const int dekey[] = {
		-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
		-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
		62, // ‘+‘
		-1, -1, -1,
		63, // ‘/‘
		52, 53, 54, 55, 56, 57, 58, 59, 60, 61, // ‘0‘-‘9‘
		-1, -1, -1, -1, -1, -1, -1,
		0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,
		13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, // ‘A‘-‘Z‘
		-1, -1, -1, -1, -1, -1,
		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, // ‘a‘-‘z‘
	};

	if (nByteSrc % 4 != 0)
		throw "bad base64 string";

	std::string pszDecode(nByteSrc * 3 / 4 + 4, ‘\0‘);
	int nLoop = pszSource[nByteSrc - 1] == ‘=‘ ? nByteSrc - 4 : nByteSrc;
	int b[4];
	int i = 0, n = 0;
	for (i = 0; i < nLoop; i += 4)
	{
		b[0] = dekey[pszSource[i]];        b[1] = dekey[pszSource[i + 1]];
		b[2] = dekey[pszSource[i + 2]];    b[3] = dekey[pszSource[i + 3]];
		if (b[0] == -1 || b[1] == -1 || b[2] == -1 || b[3] == -1)
			throw "bad base64 string";

		pszDecode[n] = (b[0] << 2) | ((b[1] & 0x30) >> 4);
		pszDecode[n + 1] = ((b[1] & 0xf) << 4) | ((b[2] & 0x3c) >> 2);
		pszDecode[n + 2] = ((b[2] & 0x3) << 6) | b[3];

		n += 3;
	}

	if (pszSource[nByteSrc - 1] == ‘=‘ && pszSource[nByteSrc - 2] == ‘=‘)
	{
		b[0] = dekey[pszSource[i]];        b[1] = dekey[pszSource[i + 1]];
		if (b[0] == -1 || b[1] == -1)
			throw "bad base64 string";

		pszDecode[n] = (b[0] << 2) | ((b[1] & 0x30) >> 4);
		pszDecode[n + 1] = ‘\0‘;
	}

	if (pszSource[nByteSrc - 1] == ‘=‘ && pszSource[nByteSrc - 2] != ‘=‘)
	{
		b[0] = dekey[pszSource[i]];        b[1] = dekey[pszSource[i + 1]];
		b[2] = dekey[pszSource[i + 2]];
		if (b[0] == -1 || b[1] == -1 || b[2] == -1)
			throw "bad base64 string";

		pszDecode[n] = (b[0] << 2) | ((b[1] & 0x30) >> 4);
		pszDecode[n + 1] = ((b[1] & 0xf) << 4) | ((b[2] & 0x3c) >> 2);
		pszDecode[n + 2] = ‘\0‘;
	}

	if (pszSource[nByteSrc - 1] != ‘=‘ && pszSource[nByteSrc - 2] != ‘=‘)
		pszDecode[n] = ‘\0‘;

	return pszDecode;
}

int main()
{
	///编码测试
	std::string encodeStr = "ONDragon";
	std::cout << "对ONDragon进行base64编码: " << b64encodestring(encodeStr) << std::endl;

	std::cout << std::endl;

	///解码测试
	std::string decodeStr = b64encodestring(encodeStr);
	std::cout << "对" << b64encodestring(encodeStr) << "进行base64解码: " << b64decodestring(decodeStr) << std::endl;

	std::cout << std::endl;

	system("pause");
	return 0;
}