Struct和Class的区别
今天这篇博文主要讲解在C++中关键字struct和class的区别。这篇博文,将会系统的将这两个关键字的不同面进行详细的讲解。
从语法上来讲,class和struct做类型定义时只有两点区别:
1.默认继承权限,如果不指定,来自class的继承按照private继承处理,来自struct的继承按照public继承处理;
2.成员的默认访问权限。class的成员默认是private权限,struct默认是public权限。以上两点也是struct和class最基本的差别,也是最本质的差别;
但是在C++中,struct进行了扩展,现在它已经不仅仅是一个包含不同数据类型的数据结构了,它包括了更多的功能。
Struct能包含成员函数吗?
是的,答案是肯定的。现在就让我写一段代码验证一下:
/* ** FileName : StructAndClassDiffDemo ** Author : Jelly Young ** Date : 2013/12/7 ** Description : More information, please go to https://www.nhooo.com */ #include <iostream> using namespace std; struct Test { int a; int getA() { return a; } void setA(int temp) { a = temp; } }; int main(int argc, char* argv[]) { Test testStruct; testStruct.setA(10); cout<<"Get the value from struct:"<<testStruct.getA()<<endl; Test *testStructPointer = new Test; testStructPointer->setA(20); cout<<"Get the value from struct again:"<<testStructPointer->getA()<<endl; delete testStructPointer; return 0; }
以上的代码会很正确的运行,是的;没错,struct能包含成员函数的。
Struct有自己的构造函数吗?
是的,可以的。看以下测试代码:
/* ** FileName : StructAndClassDiffDemo ** Author : Jelly Young ** Date : 2013/12/7 ** Description : More information, please go to https://www.nhooo.com */ #include <iostream> using namespace std; struct Test { int a; Test() { a = 100; } int getA() { return a; } void setA(int temp) { a = temp; } }; int main(int argc, char* argv[]) { Test testStruct; testStruct.setA(10); cout<<"Get the value from struct:"<<testStruct.getA()<<endl; Test *testStructPointer = new Test; testStructPointer->setA(20); cout<<"Get the value from struct again:"<<testStruct.getA()<<endl; delete testStructPointer; // test the constructor Test testConstructor; cout<<"Set the value by the construct and get it:"<<testConstructor.getA()<<endl; return 0; }
Struct可以有析构函数么?
让我来验证一下:
/* ** FileName : StructAndClassDiffDemo ** Author : Jelly Young ** Date : 2013/12/7 ** Description : More information, please go to https://www.nhooo.com */ #include <iostream> using namespace std; struct Test { int a; Test() { a = 100; } int getA() { return a; } void setA(int temp) { a = temp; } ~Test() { cout<<"Destructor function called."<<endl; } }; int main(int argc, char* argv[]) { Test testStruct; testStruct.setA(10); cout<<"Get the value from struct:"<<testStruct.getA()<<endl; Test *testStructPointer = new Test; testStructPointer->setA(20); cout<<"Get the value from struct again:"<<testStruct.getA()<<endl; delete testStructPointer; // test the constructor Test testConstructor; cout<<"Set the value by the construct and get it:"<<testConstructor.getA()<<endl; return 0; }
是的,完全支持析构函数。
Struct支持继承么?
再让我写代码验证一下:
/* ** FileName : StructAndClassDiffDemo ** Author : Jelly Young ** Date : 2013/12/7 ** Description : More information, please go to https://www.nhooo.com */ #include <iostream> using namespace std; struct A { int a; A() { a = 10; } void print() { cout<<"I am from A"<<endl; } }; struct B : A { int b; B() { a = 30; // set a to 30 b = 20; } /*void print() { cout<<"I am from B"<<endl; }*/ }; int main(int argc, char* argv[]) { B b1; cout<<b1.a<<endl; cout<<b1.b<<endl; b1.print(); A a1; cout<<a1.a<<endl; a1.print(); return 0; }
运行上述代码,struct支持继承。
Struct支持多态么?
写代码测试一下便知:
/* ** FileName : StructAndClassDiffDemo ** Author : Jelly Young ** Date : 2013/12/7 ** Description : More information, please go to https://www.nhooo.com */ #include <iostream> using namespace std; struct A { virtual void print() = 0; }; struct B : A { void print() { cout<<"I am from B"<<endl; } }; struct C : A { void print() { cout<<"I am from C"<<endl; } }; int main(int argc, char* argv[]) { A *a1; B *b1 = new B; C *c1 = new C; a1 = b1; a1->print(); // call B, not A a1 = c1; a1->print(); // call C, not A return 0; }
Struct支持Private、Protected和Public关键字么?
/* ** FileName : StructAndClassDiffDemo ** Author : Jelly Young ** Date : 2013/12/7 ** Description : More information, please go to https://www.nhooo.com */ #include <iostream> using namespace std; struct A { private: int b; protected: int c; public: A() { b = 10; c = 20; d = 30; } int d; }; struct B : A { void printA_C() { cout<<A::c<<endl; }; // private member can not see /*void printA_B() { cout<<A::b<<endl; }*/ void printA_D() { cout<<A::d<<endl; } }; int main(int argc, char* argv[]) { A a1; B b1; // private member can not see //cout<<a1.b<<endl; // protected member can not see //cout<<a1.c<<endl; // public member can see cout<<a1.d<<endl; return 0; }
写了这么多了,那么会出现这种一个状况,如果是class的父类是struct关键字描述的,那么默认访问属性是什么?
当出现这种情况时,到底默认是public继承还是private继承,取决于子类而不是基类。class可以继承自struct修饰的类;同时,struct也可以继承自class修饰的类,继承属性如下列描述:
class B:A{}; // private 继承 class A{}; struct B:A{}; // public 继承
最后,那么到底是使用struct,还是使用class呢?这个看个人喜好,但是这里有一个编程规范的问题,当你觉得你要做的更像是一种数据结构的话,那么用struct,如果你要做的更像是一种对象的话,那么用class。
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