Struct和Class的區別
今天這篇博文主要講解在C++中關鍵字struct和class的區別。這篇博文，將會系統的將這兩個關鍵字的不同面進行詳細的講解。
從語法上來講，class和struct做類型定義時只有兩點區別：
1.默認繼承權限，如果不指定，來自class的繼承按照private繼承處理，來自struct的繼承按照public繼承處理；
2.成員的默認訪問權限。class的成員默認是private權限，struct默認是public權限。以上兩點也是struct和class最基本的差別，也是最本質的差別；
但是在C++中，struct進行了擴展，現在它已經不僅僅是一個包含不同數據類型的數據結構了，它包括了更多的功能。
Struct能包含成員函數嗎？
是的，答案是肯定的。現在就讓我寫一段代碼驗證一下：
/*
** FileName : StructAndClassDiffDemo
** Author : Jelly Young
** Date : 2013/12/7
** Description : More information, please go to //m.survivalescaperooms.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;
}
以上的代碼會很正確的運行，是的；沒錯，struct能包含成員函數的。
Struct有自己的構造函數嗎？
是的，可以的。看以下測試代碼：
/*
** FileName : StructAndClassDiffDemo
** Author : Jelly Young
** Date : 2013/12/7
** Description : More information, please go to //m.survivalescaperooms.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可以有析構函數么？
讓我來驗證一下：
/*
** FileName : StructAndClassDiffDemo
** Author : Jelly Young
** Date : 2013/12/7
** Description : More information, please go to //m.survivalescaperooms.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，完全支持析構函數。
Struct支持繼承么？
再讓我寫代碼驗證一下：
/*
** FileName : StructAndClassDiffDemo
** Author : Jelly Young
** Date : 2013/12/7
** Description : More information, please go to //m.survivalescaperooms.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;
}
運行上述代碼，struct支持繼承。
Struct支持多態么？
寫代碼測試一下便知：
/*
** FileName : StructAndClassDiffDemo
** Author : Jelly Young
** Date : 2013/12/7
** Description : More information, please go to //m.survivalescaperooms.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關鍵字么？
/*
** FileName : StructAndClassDiffDemo
** Author : Jelly Young
** Date : 2013/12/7
** Description : More information, please go to //m.survivalescaperooms.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;
}
寫了這么多了，那么會出現這種一個狀況，如果是class的父類是struct關鍵字描述的，那么默認訪問屬性是什么？
當出現這種情況時，到底默認是public繼承還是private繼承，取決于子類而不是基類。class可以繼承自struct修飾的類；同時，struct也可以繼承自class修飾的類，繼承屬性如下列描述：
class B:A{}; // private 繼承
class A{};
struct B:A{}; // public 繼承
最后，那么到底是使用struct，還是使用class呢？這個看個人喜好，但是這里有一個編程規范的問題，當你覺得你要做的更像是一種數據結構的話，那么用struct，如果你要做的更像是一種對象的話，那么用class。
