Constructor usage rules for C + + classes

//constructor usage rules for classes#define_crt_secure_no_warnings#include<iostream>using namespacestd;classpointa{};classpointb{ Public: Pointb (intAarint_b,Const Char*pin/*inch*/) {x=_a; Y=_b; Remark= (Char*)malloc(sizeof(Char) * (strlen (PIN) +1));        strcpy (remark, PIN); cout<<"I'm a self-defined, parametric constructor. 4"<<Endl; }Private:    intx; inty; Char*remark;};classpointc{ Public: Pointc (POINTC&pm) {cout<<"I'm a custom copy constructor 3"<<Endl; //Modifying a copy constructorx =pm.x; Y=pm.y; //remark = Pm.remark; This sentence is wrong.//Modified ScenarioRemark = (Char*)malloc(sizeof(Char) * (strlen (Pm.remark) +1));    strcpy (remark, Pm.remark); }Private:    intx; inty; Char*remark;};voidProtecta () {Pointa P1;//Call the default parameterless constructorPointa P2=p1;//Call the default copy constructor// Conclusion ①: When no one constructor is defined in a class, the C + + compiler provides a parameterless constructor and a copy constructor//POINTB P3;//Error : Error C2512: "POINTB": no appropriate default constructor availablePOINTB P4 (3,3,"455");//calling a custom-defined parameter constructorPOINTB P5 = P4;//Call the default copy constructor// Conclusion ②: When an arbitrary non-copy constructor is defined in a class (no parameter, no parameter), the C + + compiler does not provide a parameterless constructor.//However, if any copy function is not defined in the class, the C + + compiler will still provide a default copy constructor//POINTC P6;//Error C2512: "POINTC": no appropriate default constructor available// Conclusion ③: When a copy function is defined in a class, the C + + compiler does not provide a default parameterless constructor// Conclusion ④: The default copy constructor is simply a simple assignment between class member variables (a shallow copy of the details reference class)}voidMain () {System ("Pause");}

Constructor usage rules for C + + classes