in_addr,char* ,unsigned long 之间的互相转换
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在网络编程中经常会用到in_addr,char* ,unsigned long表示的IP地址（指定的是IP4），winsock 提供inet_addr（char* -> unsigned long），inet_ntoa（in_addr -> char*），在实际应用中，不同数据类型总是需要转换，如果每一次转换需要调用函数转换，这样会很繁琐。
通常，一个IP（v4）地址是一个32位无符号的整数类型，即unsigned long，而in_addr结构可以用来表现每个8位的数值（u_char），in_addr结构实际上也是一个32位无符号的整数类型，也就是in_addr::S_un::S_addr,这样in_addr可以和unsigned long直接转换。为了便于阅读，并提供了char*的形式来表示ip地址。inet_addr用于从 char* 类型到 unsigned long的转换；inet_ntoa提供了从in_addr -> char*的转换。
虽然 in_addr,char* ,unsigned long之间可以通过函数来转换，但编写代码的过程很繁琐，几乎每一次转换调用都需要调用函数，而且很容易忘记函数。既然这几个类型可以互相转换，那就可以通过一个类来封装这些类型，使得这些类型可以在类的封装下实现互相转换。
下面使用一个命名为CIPv4AddressForm的类封装上述的三种数据类型，并在类实现几个常用的方法，比如得到数据成员的数值、在不同类型之间直接转换(实现运算符重载)，不同数据类型之间直接赋值。
//定义
class CIPv4AddressForm{ protected: char* m_pc; in_addr m_addr; unsigned long m_ul; public: inline CIPv4AddressForm(){} CIPv4AddressForm(char* IpAddress); CIPv4AddressForm(unsigned long& IpAddress); CIPv4AddressForm(in_addr IpAddress); CIPv4AddressForm(CIPv4AddressForm& ins); virtual ~CIPv4AddressForm(); /*重新设置*/ CIPv4AddressForm& Reset(char* IpAddress); CIPv4AddressForm& Reset(unsigned long& IpAddress); CIPv4AddressForm& Reset(in_addr IpAddress); /*获取类型*/ char* ToString()const; unsigned long ToUInt() ; in_addr& ToAddr(); /*自动转换*/ operator unsigned long(); operator char* ()const; operator in_addr& (); /*比较是否相等*/ bool operator ==(CIPv4AddressForm& r ); bool operator ==(char* r); bool operator ==(in_addr& r); bool operator ==(unsigned long& r); bool operator !=(CIPv4AddressForm& r); bool operator !=(char* r); bool operator !=(in_addr& r); bool operator !=(unsigned long& r); /*赋值*/ CIPv4AddressForm& operator =(CIPv4AddressForm& r); CIPv4AddressForm& operator =(char* r); CIPv4AddressForm& operator =(unsigned long& r); CIPv4AddressForm& operator =(in_addr& r); };//实现
CIPv4AddressForm::CIPv4AddressForm(in_addr IpAddress){ this->m_addr=IpAddress; this->m_ul=this->m_addr.S_un.S_addr; this->m_pc=inet_ntoa(this->m_addr); } CIPv4AddressForm::CIPv4AddressForm(unsigned long& IpAddress){ this->m_ul=IpAddress; this->m_addr.S_un.S_addr=IpAddress; this->m_pc=inet_ntoa(this->m_addr); } CIPv4AddressForm::CIPv4AddressForm(char* IpAddress){ this->m_ul=inet_addr(IpAddress); this->m_addr.S_un.S_addr=this->m_ul; this->m_pc=inet_ntoa(this->m_addr);//不要直接 this->m_pc=IpAddress,否则IpAddress释放了m_pc就没作用了 } CIPv4AddressForm::CIPv4AddressForm(CIPv4AddressForm& ins){ this->m_ul=ins.ToUInt(); this->m_addr.S_un.S_addr=this->m_ul; this->m_pc=inet_ntoa(this->m_addr); } CIPv4AddressForm::~CIPv4AddressForm(){ //no implement... } /*重新设置*/ CIPv4AddressForm& CIPv4AddressForm::Reset(in_addr IpAddress){ this->m_addr=IpAddress; this->m_ul=this->m_addr.S_un.S_addr; this->m_pc=inet_ntoa(this->m_addr); return (*this); } CIPv4AddressForm& CIPv4AddressForm::Reset(unsigned long& IpAddress){ this->m_ul=IpAddress; this->m_addr.S_un.S_addr=IpAddress; this->m_pc=inet_ntoa(this->m_addr); return (*this); } CIPv4AddressForm& CIPv4AddressForm::Reset(char* IpAddress){ this->m_ul=inet_addr(IpAddress); this->m_addr.S_un.S_addr=this->m_ul; this->m_pc=inet_ntoa(this->m_addr);//不要直接 this->m_pc=IpAddress return (*this); } /*获取类型*/ char* CIPv4AddressForm::ToString()const{ return this->m_pc; } unsigned long CIPv4AddressForm::ToUInt(){ return this->m_ul; } in_addr& CIPv4AddressForm::ToAddr(){ return this->m_addr; } /*自动转换*/ CIPv4AddressForm::operator unsigned long(){ return this->m_ul; } CIPv4AddressForm::operator char *()const{ return this->m_pc; } CIPv4AddressForm::operator in_addr &(){ return this->m_addr; } /*比较是否相等*/ bool CIPv4AddressForm::operator ==(CIPv4AddressForm &r){ if(this->m_ul==r.ToUInt()) return true; return false; } bool CIPv4AddressForm::operator ==(char* r){ if(lstrcmpiA(r,this->m_pc)==0) return true; return false; } bool CIPv4AddressForm::operator ==(unsigned long& r){ if(this->m_ul==r) return true; return false; } bool CIPv4AddressForm::operator ==(in_addr &r){ if(this->m_addr.S_un.S_addr==r.S_un.S_addr) return true; return false; } bool CIPv4AddressForm::operator !=(CIPv4AddressForm &r){ if(this->m_ul!=r.ToUInt()) return true; return false; } bool CIPv4AddressForm::operator !=(char* r){ if(lstrcmpiA(r,this->m_pc)!=0) return true; return false; } bool CIPv4AddressForm::operator !=(unsigned long& r){ if( this->m_ul!=r) return true; return false; } bool CIPv4AddressForm::operator !=(in_addr &r){ if(this->m_addr.S_un.S_addr!=r.S_un.S_addr) return true; return false; }/*赋值*/ CIPv4AddressForm& CIPv4AddressForm::operator =(CIPv4AddressForm& r){ this->m_ul=r.ToUInt(); this->m_addr.S_un.S_addr=this->m_ul; this->m_pc=inet_ntoa(this->m_addr); return (*this); } CIPv4AddressForm& CIPv4AddressForm::operator =(char* r){ this->m_ul=inet_addr(r); this->m_addr.S_un.S_addr=this->m_ul; this->m_pc=inet_ntoa(this->m_addr); return (*this); } CIPv4AddressForm& CIPv4AddressForm::operator =(unsigned long & r){ this->m_ul=r; this->m_addr.S_un.S_addr=r; this->m_pc=inet_ntoa(this->m_addr); return(*this); } CIPv4AddressForm& CIPv4AddressForm::operator =(in_addr& r){ this->m_addr=r; this->m_ul=this->m_addr.S_un.S_addr; this->m_pc=inet_ntoa(this->m_addr); return (*this); }上述的封装类简化了ip地址在不同数据类型之间转换在编码时的重复劳动，但程序的运行效率就会比原来的直接调用要低一点。
调用 示例：
CIPv4AddressForm ins("192.168.0.10");
std::cout<<ins.ToUInt()<<std::endl;
CIPv4AddressForm ins3;
ins3=ins;
std::cout<<ins3.ToString()<<std::endl;
ins3="168.192.0.1";
PCL(ins3.ToString());
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