C++ Tutorial/Operators statements/sizeof — различия между версиями
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Текущая версия на 10:30, 25 мая 2010
Содержание
Demonstrate sizeof.
#include <iostream>
using namespace std;
int main()
{
char ch;
int i;
cout << sizeof ch << " "; // size of char
cout << sizeof i << " "; // size of int
cout << sizeof (float) << " "; // size of float
cout << sizeof (double) << " "; // size of double
return 0;
}1 4 4 8
Object sizes
#include <iostream>
using std::cout;
using std::endl;
class Box {
public:
Box() :length(1.0), width(1.0), height(1.0), pMaterial("new") {}
int totalSize() {
return sizeof(length) + sizeof(width) + sizeof(height) + sizeof(pMaterial
);
}
private:
char* pMaterial;
double length;
double width;
double height;
};
int main() {
Box box;
Box boxes[10];
cout << endl << "The data members of a Box object occupy "
<< box.totalSize() << " bytes.";
cout << endl << "A single Box object occupies "
<< sizeof (Box) << " bytes.";
cout << endl << "An array of 10 Box objects occupies "
<< sizeof(boxes) << " bytes."
<< endl;
return 0;
}The data members of a Box object occupy 28 bytes. A single Box object occupies 32 bytes. An array of 10 Box objects occupies 320 bytes.
sizeof a class
/* The following code example is taken from the book
* "C++ Templates - The Complete Guide"
* by David Vandevoorde and Nicolai M. Josuttis, Addison-Wesley, 2002
*
* (C) Copyright David Vandevoorde and Nicolai M. Josuttis 2002.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include <iostream>
class EmptyClass {
};
int main()
{
std::cout << "sizeof(EmptyClass): " << sizeof(EmptyClass)
<< "\n";
}sizeof(EmptyClass): 1
sizeof a union
#include<iostream.h>
union u_tag{
int i;
double d;
}u={88};
struct s_tag{
int i;
double d;
}s={66,1.234};
int main()
{
int size;
size=sizeof(union u_tag);
cout<<"sizeof(union u_tag)="<<size<<endl;
u.i=100;
cout<<"u.i="<<u.i<<endl;
u.d=1.2345;
cout<<"u.d="<<u.d<<endl;
size=sizeof(u.d);
cout<<"sizeof(u.d)="<<size<<endl;
cout<<"s.i="<<s.i<<endl;
cout<<"s.d="<<s.d<<endl;
size=sizeof(struct s_tag);
cout<<"sizeof(struct s_tag)="<<size<<endl;
}sizeof(union u_tag)=8 u.i=100 u.d=1.2345 sizeof(u.d)=8 s.i=66 s.d=1.234 sizeof(struct s_tag)=16
Use sizeof operator on an array name: returns the number of bytes in the array
#include <iostream>
using std::cout;
using std::endl;
int main()
{
double array[ 20 ];
cout << "The number of bytes in the array is " << sizeof( array );
return 0;
}The number of bytes in the array is 160
Using the sizeof operator for base class and derived class
#include <iostream>
#include <ostream>
class base {};
class derived : public base {};
int main()
{
using namespace std;
cout << sizeof(base) << "\n";
cout << sizeof(derived) << "\n";
base b[3];
cout << sizeof(b) << "\n";
derived d[5];
cout << sizeof(d) << "\n";
}1 1 3 5
