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.jb51.net
*/
#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.jb51.net
*/
#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.jb51.net
*/
#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.jb51.net
*/
#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.jb51.net
*/
#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.jb51.net
*/
#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。
