base64

使用SMTP发送邮件需要用到base64编码和解码，这里是char类型的字符串转换，如果需要编码包括特殊字符的文字，如\0等，请自行修改，将入口参数换成(char* pStr, int iLen), 内部稍作修改。

const unsigned char * base64 = (unsigned char*)"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";  

static CStringA base64encode(CStringA str)
{
	CStringA cRet;

	int iStrLen = str.GetLength();
	int iOutLen = 0;
	if (iStrLen % 3 == 0)
	{
		iOutLen = iStrLen / 3 * 4;
	}
	else
	{
		iOutLen = iStrLen /3 * 4 + 4;
	}

	unsigned char* pBuffer = new unsigned char [iStrLen + 1];
	unsigned char* pOut = new unsigned char [iOutLen + 1];

	memcpy(pBuffer, str.GetBuffer(0), iStrLen);
	str.ReleaseBuffer();
	pBuffer[iStrLen] = 0;
	memset(pOut, 0, iOutLen);

	int i = 0;
	int j = 0;
	for (i = 0, j = 0; i < iStrLen -3; i += 3, j += 4)
	{
         pOut[j + 0] = (pBuffer[i] & 0xFC)>>2;
         pOut[j + 1] = ((pBuffer[i] & 0x03)<<4) + ((pBuffer[i + 1] &0xF0) >> 4);
         pOut[j + 2] = ((pBuffer[i + 1] & 0x0F) << 2) + ((pBuffer[i + 2] & 0xC0) >> 6);
         pOut[j + 3] = pBuffer[i + 2] & 0x3F;
	}

	if (iStrLen % 3 == 1)
	{
         pOut[j + 0] = (pBuffer[i] & 0xFC) >> 2;
         pOut[j + 1] = ((pBuffer[i] & 0x03) << 4);
         pOut[j + 2] = 64;
         pOut[j + 3] = 64;
         j += 4;
	}
	else if (iStrLen % 3 == 2)
	{
         pOut[j + 0] = (pBuffer[i] & 0xFC) >> 2;
         pOut[j + 1] = ((pBuffer[i] & 0x03) << 4)+((pBuffer[i + 1] & 0xF0) >> 4);
         pOut[j + 2] = ((pBuffer[i + 1] & 0x0F) << 2);
         pOut[j + 3] = 64;
         j+=4;
	}
	else
	{
         pOut[j + 0] = (pBuffer[i] & 0xFC)>>2;
         pOut[j + 1] = ((pBuffer[i] & 0x03)<<4) + ((pBuffer[i + 1] &0xF0) >> 4);
         pOut[j + 2] = ((pBuffer[i + 1] & 0x0F) << 2) + ((pBuffer[i + 2] & 0xC0) >> 6);
         pOut[j + 3] = pBuffer[i + 2] & 0x3F;
		 j += 4;
	}

	for (int i = 0; i < iOutLen; i++)
	{
		pOut[i] = base64[pOut[i]];
	}
	pOut[iOutLen] = 0;

	cRet = pOut;
	delete [iStrLen + 1] pBuffer;
	pBuffer = NULL;
	delete [iOutLen + 1] pOut;
	pOut = NULL;

	return cRet;
}
   
static CStringA base64decode(CStringA str)
{
	CStringA cRet;
	
	int iStrLen = str.GetLength();
	int iOutLen = iStrLen * 3 / 4;

	unsigned char* pBuffer = new unsigned char [iStrLen + 1];
	unsigned char* pOut = new unsigned char [iOutLen + 1];

	memcpy(pBuffer, str.GetBuffer(0), iStrLen);
	str.ReleaseBuffer();
	pBuffer[iStrLen] = 0;
	memset(pOut, 0, iOutLen);

	CStringA tmp(base64);
	for (int i = 0; i < iStrLen; i++)
	{
		pBuffer[i] = tmp.Find(pBuffer[i]);
	}

	unsigned char* pEnd = &pBuffer[iStrLen - 1];
	while (*pEnd == 64)
	{
		*pEnd = 0;
		pEnd--;
		if (pEnd == pBuffer)
		{
			break;
		}
	}

	int i = 0;
	int j = 0;
	for(i = 0, j = 0; i < iStrLen; i += 4, j += 3)
	{
         pOut[j + 0] = (pBuffer[i] << 2) + ((pBuffer[i + 1] & 0x30) >> 4);
         pOut[j + 1] = ((pBuffer[i + 1] & 0x0F) << 4) + ((pBuffer[i + 2] & 0x3C) >> 2);
         pOut[j + 2] = ((pBuffer[i + 2] & 0x03) << 6) + pBuffer[i + 3];
	}
	pOut[j] = 0;

	cRet = pOut;

	delete [iStrLen + 1] pBuffer;
	pBuffer = NULL;
	delete [iOutLen + 1] pOut;
	pOut = NULL;

	return cRet;
}