如有一个如下类:
class EquipmentPiece { private: int IDNumber; public: EquipmentPiece(int IDNumber) : IDNumber(IDNumber) {}; };
以下列出几种初始化的方法:
<一>、对象数组
int ID1, ID2, ID3; EquipmentPiece bestPieces[] = { EquipmentPiece(ID1), EquipmentPiece(ID2), EquipmentPiece(ID3) };
注意:
EquipmentPiece bestPieces[10]; //no appropriate default constructor available EquipmentPiece *bestPieces = new EquipmentPiece[10]; //no appropriate default constructor available
当然,如果你将构造函数参数全都设了默认值,以上两种写法也成功,如将类中构造函数修改如下: ... EquipmentPiece(int IDNumber = 0) : IDNumber(IDNumber) {}; ...
<二>、指针数组
typedef EquipmentPiece* PEP; //PEP是个指向EquipmentPiece的指针
PEP bestPieces[10]; //等同于 PEP *bestPieces = new PEP[10];
//然后初始化 for(int i = 0; i < 10; i++){ bestPieces[i] = new EquipmentPiece( IDNumber ); }
注意: 要记得将此数组所指的所有对象删除。如果忘了会产生资源泄露。还有就是该方法与对象数组相比需要额外内存用于存放指针。(过度使用内存 这一问题可以避免,见第三种方法)
<三>、使用placement new(定位new操作符)
方法是:先为此数组分配raw memory,然后使用"placement new"在这块内存上构造EquipmentPiece objects;
//分配足够的raw memory,给一个预备容纳10个EquipmentPiece objects的数组使用 void *rawMemory = operator new(10*sizeof(EquipmentPiece));
//让bestPieces指向此内存,使这块内存被视为一个EquipmentPiece数组 EquipmentPiece *bestPieces = reinterpret_cast<EquipmentPiece*>(rawMemory);
//利用"placement new"构造这块内存中的EquipmentPiece objects。 int IDNumber = 0; for(int i = 0; i < 10; i++){ new (&bestPieces[i]) EquipmentPiece( IDNumber ); }
注意:该方法维护比较困难。在数组内对象结束生命时,要以手动方式调用destructors,最后还得调用operator delete释放raw memory。
//将bestPieces中对象以构造次序的反序析构掉 for(i = 0; i < 10; i++){ bestPieces[i].~EquipmentPiece(); }
//释放raw memory operator delete (rawMemory);