Zero-overhead principle
1、C++的design是遵循Zero-overhead principle，作为programmer，在开发的时候，也需要遵循zero overhead principle，即"You don't pay for what you don't use"
2、C++ Zero-overhead principle其实就是optimization principle
3、能够体现zero overhead的例子:
a、C++ data model: object的memory不会占用超过data member，C++没有额外导致它的扩大
b、
template<typename RspFieldType>
struct CRspFieldUnpackerBase: CRspUnpackerBase
{
private:
using BaseClass = CRspUnpackerBase;
protected:
CRspFieldUnpackerBase(CRspMsg &Msg) :
BaseClass { Msg }
{
if (this->m_Msg.IsResponse()) // 如果不是正确应答，GetBizFixed已经调用过了
{
this->m_Rsp = reinterpret_cast<RspFieldType*>(this->m_Msg.m_lpMsgReader->GetBizFixed());
}
}
RspFieldType *m_Rsp { nullptr };
public:
/**
* @brief 获得响应字段
*
* @return
*/
RspFieldType* Get()
{
return this->m_Rsp;
}
std::ostream& Print(std::ostream &Stream) override
{
if (this->m_Rsp)
{
Stream << "消息体:" << m_Rsp << ";";
}
return Stream;
}
};
/**
* @brief 对response field进行解包
*
* @tparam RspFieldType
* @tparam Enable
*/
template<typename RspFieldType, typename Enable = void>
struct CRspFieldUnpacker: CRspFieldUnpackerBase<RspFieldType>
{
private:
using BaseClass = CRspFieldUnpackerBase<RspFieldType>;
public:
CRspFieldUnpacker(CRspMsg &Msg) :
BaseClass { Msg }
{
}
};
template<typename RspFieldType>
struct CRspFieldUnpacker<RspFieldType, typename std::enable_if<has_member_ErrorMsg<RspFieldType>::value && has_member_ErrorID<RspFieldType>::value>::type> : virtual CRspFieldUnpackerBase<RspFieldType>
{
private:
using BaseClass = CRspFieldUnpackerBase<RspFieldType>;
public:
CRspFieldUnpacker(CRspMsg &Msg) :
BaseClass { Msg }
{
/**
* 只有在ErrorID 非0，即存在错误的情况下，才进行转换
*/
if (m_RspField.ErrorID != 0)
{
/**
* 需要进行一次deep copy
*/
m_RspField = *(this->m_Rsp);
int Ret = ::GbkToUtf8(this->m_Rsp->ErrorMsg, std::strlen(this->m_Rsp->ErrorMsg), m_RspField.ErrorMsg, sizeof(m_RspField.ErrorMsg));
if (Ret == 0)
{
LOG_DEBUG("GBK->UTF8转换成功");
}
else
{
LOG_ERROR("GBK->UTF8转换失败");
}
this->m_Rsp = &m_RspField;
}
}
private:
RspFieldType m_RspField;
};