gbk转换到utf8

std::string gb2utf8(const std::string strGBK)
{	
	const char *str = strGBK.c_str();
	const unsigned int CP_GBK = 936;
	int len = MultiByteToWideChar(CP_GBK, 0, str, -1, NULL, 0);
	wchar_t* buf1 = new wchar_t[len + 1];
	memset(buf1, 0, (len + 1)* sizeof(wchar_t));
	MultiByteToWideChar(CP_GBK, 0, str, -1, buf1, len);

	len = WideCharToMultiByte(CP_UTF8, 0, buf1, -1, NULL, 0, NULL, NULL);
	char* buf2 = new char[len + 1];
	memset(buf2, 0, len + 1);
	WideCharToMultiByte(CP_UTF8, 0, buf1, -1, buf2, len, NULL, NULL);
	std::string ret = buf2;
	delete[] buf1;
	delete[] buf2;

	return ret;
}