Posted on 2012-03-12 10:18
C小加 閱讀(2134)
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C++和面向?qū)ο?/a>
//此代碼在32位win下運(yùn)行成功
#include<iostream>
using namespace std;
class A//A是空類，編譯器會(huì)用一個(gè)char類型標(biāo)記這個(gè)類，大小為1
{
};
class B:public A//B繼承了A，但同樣也是空類，大小為1
{
};
class C:virtual public A//虛擬繼承的時(shí)候編譯器會(huì)安插一個(gè)指向父類的指針，大小為4
{
};
class D//大小為4
{
public:
int a;
static int b;//靜態(tài)變量被放在靜態(tài)存儲(chǔ)區(qū)
};
class E //print函數(shù)不占內(nèi)存空間，大小為4
{
public:
void print(){cout<<"E"<<endl;}
private:
int a;
};
class F//虛函數(shù)會(huì)占用一個(gè)指針大小的內(nèi)存，系統(tǒng)需要用這個(gè)指針維護(hù)虛函數(shù)表。大小為8
{
public:
virtual void print(){cout<<"F"<<endl;}
private:
int a;
};
class G:public F//多了一個(gè)虛函數(shù)內(nèi)存大小不變，可見一個(gè)類只有一個(gè)虛函數(shù)指針。大小為8
{
public:
virtual void print(){cout<<"G"<<endl;}
virtual void print2(){cout<<"G2"<<endl;}
};
int main()
{
A a;
B b;
C c;
D d;
E e;
F f;
G g;
cout<<sizeof(A)<<" "<<sizeof(a)<<endl;//1 1
cout<<sizeof(B)<<" "<<sizeof(b)<<endl;//1 1
cout<<sizeof(C)<<" "<<sizeof(c)<<endl;//4 4
cout<<sizeof(D)<<" "<<sizeof(d)<<endl;//4 4
cout<<sizeof(E)<<" "<<sizeof(e)<<endl;//4 4
cout<<sizeof(F)<<" "<<sizeof(f)<<endl;// 8 8
cout<<sizeof(G)<<" "<<sizeof(g)<<endl;//8 8
return 0;
}