【C++】代码实现：base64 编码与解码

• base64 编码函数代码：

// Base64 编码
void Base64Encode(const std::string &input, std::string &output)
{
	//编码表
	const char EncodeTable[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

	//返回值
	size_t DataByte = input.size();
	const char* Data = input.data();
	std::string strEncode;
	unsigned char Tmp[4] = { 0 };
	int LineLength = 0;
	for (int i = 0; i < (int)(DataByte / 3); i++)
	{
		Tmp[1] = *Data++;
		Tmp[2] = *Data++;
		Tmp[3] = *Data++;
		strEncode += EncodeTable[Tmp[1] >> 2];
		strEncode += EncodeTable[((Tmp[1] << 4) | (Tmp[2] >> 4)) & 0x3F];
		strEncode += EncodeTable[((Tmp[2] << 2) | (Tmp[3] >> 6)) & 0x3F];
		strEncode += EncodeTable[Tmp[3] & 0x3F];
		if (LineLength += 4, LineLength == 76) { strEncode += "\r\n"; LineLength = 0; }
	}

	//对剩余数据进行编码
	int Mod = DataByte % 3;
	if (Mod == 1)
	{
		Tmp[1] = *Data++;
		strEncode += EncodeTable[(Tmp[1] & 0xFC) >> 2];
		strEncode += EncodeTable[((Tmp[1] & 0x03) << 4)];
		strEncode += "==";
	}
	else if (Mod == 2)
	{
		Tmp[1] = *Data++;
		Tmp[2] = *Data++;
		strEncode += EncodeTable[(Tmp[1] & 0xFC) >> 2];
		strEncode += EncodeTable[((Tmp[1] & 0x03) << 4) | ((Tmp[2] & 0xF0) >> 4)];
		strEncode += EncodeTable[((Tmp[2] & 0x0F) << 2)];
		strEncode += "=";
	}

	output = strEncode;
}

• base64 解码函数代码：

// Base64 解码
void Base64Decode(const std::string &input, std::string &output)
{
	//解码表
	const char DecodeTable[] =
	{
		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
		62, // '+'
		0, 0, 0,
		63, // '/'
		52, 53, 54, 55, 56, 57, 58, 59, 60, 61, // '0'-'9'
		0, 0, 0, 0, 0, 0, 0,
		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'
		0, 0, 0, 0, 0, 0,
		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'
	};

	//返回值
	std::string strDecode;
	size_t DataByte = input.size();
	const char* Data = input.data();
	int nValue;
	size_t i = 0;
	while (i < DataByte)
	{
		if (*Data != '\r' && *Data != '\n')
		{
			nValue = DecodeTable[*Data++] << 18;
			nValue += DecodeTable[*Data++] << 12;
			strDecode += (nValue & 0x00FF0000) >> 16;
			if (*Data != '=')
			{
				nValue += DecodeTable[*Data++] << 6;
				strDecode += (nValue & 0x0000FF00) >> 8;
				if (*Data != '=')
				{
					nValue += DecodeTable[*Data++];
					strDecode += nValue & 0x000000FF;
				}
			}
			i += 4;
		}
		else// 回车换行,跳过
		{
			Data++;
			i++;
		}
	}
	output = strDecode;
}