class A; class B { A m_a; public:B(A a) :m_a(a) { } }; cla

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class A; class B { A *m_a; public:B(A *a) :m_a(a) { } }; class A { A() :b(this) { } B b; };
这段代码中A() :b(this)
这句话不是对成员变量b进行初始化吗
但是在B类中没有无参数的构造函数这段代码我看不懂

$class A; class B { A *m_a; public:B(A *a) :m_a(a) { } }; cla$

用extern 引进变量
如在C...View类中写一行
extern C...App theApp;
那么这行下面的函数中都可以使用theApp这个变量了.（theApp是C...App类定义的变量,先在原类的实现中定义一个变量,再在别的类的实现中用extern,即在C...App.cpp先定义C...App theApp;）.

class A; class B { A *m_a; public:B(A *a) :m_a(a) { } }; cla #include class A { public: int n; }; class B:virtual public public class a { c++中,class C:public A,B和class C:public A,public B有什么区别? It time for ____. a,clsss b ,have class,c,to class,d,has cla class A{ int a; public:A(const A& rhs){.} A b=(*this);////// public class test(){ public Class a(int i) {} public static public abstract class A implements B不太理解 We are going to have an exam _____.A:in the class B:in a cla C# class A {} class B:A {} class C:B Main() { A a = new A; B class A{int i,j;public:static int x;public:A(int a = 0,int b #include class A { public:void print1() { cout