в 14:21, 25 мая 2010

2010-05-25T14:21:17Z

Admin: 1 версия: Импорт контента...

2010-05-25T10:29:28Z

1 версия: Импорт контента...

Новая страница

==A friend function==

<source lang="cpp">#include <iostream>
using namespace std;

class MyClass {
int a, b;
public:
MyClass(int i, int j) { a=i; b=j; }
friend int friendFunction(MyClass x); // a friend function
};

// friendFunction() is a not a member function of any class.
int friendFunction(MyClass x)
{
/* Because friendFunction() is a friend of MyClass, it can
directly access a and b. */
int max = x.a < x.b ? x.a : x.b;

return max;
}

int main()
{
MyClass n(18, 111);

cout << "friendFunction(n) is " << friendFunction(n) << "\n";

return 0;
}</source>
<pre class=codeResult>friendFunction(n) is 18</pre>

==A function can be a member of one class and a friend of another==

<source lang="cpp">#include <iostream>
using namespace std;

class Cylinder; // a forward declaration

enum colors { red, green, yellow };

class Cube {
colors color;
public:
Cube(colors c) { color= c; }
bool sameColor(Cylinder y);
};

class Cylinder {
colors color;
public:
Cylinder(colors c) { color = c; }
friend bool Cube::sameColor(Cylinder y);
};

bool Cube::sameColor(Cylinder y) {
if(color == y.color)
return true;
else
return false;
}

int main()
{
Cube cube1(red);
Cube cube2(green);
Cylinder cyl(green);

if(cube1.sameColor(cyl))
cout << "cube1 and cyl are the same color.\n";
else
cout << "cube1 and cyl are different colors.\n";

if(cube2.sameColor(cyl))
cout << "cube2 and cyl are the same color.\n";
else
cout << "cube2 and cyl are different colors.\n";

return 0;
}</source>
<pre class=codeResult>cube1 and cyl are different colors.
cube2 and cyl are the same color.</pre>

==Friend functions and operator overloading==

<source lang="cpp">#include <iostream>
#include <string>
using namespace std;
class MyClass
{
friend void Peek(const MyClass& aMyClass);
friend ostream& operator<<(ostream& os, const MyClass& aMyClass);
public:
MyClass(const string& name = "");
private:
string m_Name;
};
MyClass::MyClass(const string& name):
m_Name(name)
{}
void Peek(const MyClass& aMyClass);
ostream& operator<<(ostream& os, const MyClass& aMyClass);
int main()
{
MyClass myObject("A");
Peek(myObject);
cout << myObject;
return 0;
}
void Peek(const MyClass& aMyClass)
{
cout << aMyClass.m_Name << endl;
}
ostream& operator<<(ostream& os, const MyClass& aMyClass)
{
os << "MyClass Object - ";
os << "m_Name: " << aMyClass.m_Name;
return os;
}</source>

==Friend functions can access private members of a class==

<source lang="cpp">#include <iostream>
using std::cout;
using std::endl;
class MyClass
{
friend void setX( MyClass &, int ); // friend declaration
public:
MyClass() : x( 0 )
{
}
void print() const
{
cout << x << endl;
}
private:
int x;
};
void setX( MyClass &c, int val )
{
c.x = val;
}
int main()
{
MyClass counter;
counter.print();
setX( counter, 8 );
counter.print();
return 0;
}</source>
<pre class=codeResult>0
8</pre>

==Friend functions can be shared by two or more classes==

<source lang="cpp">#include <iostream>
using namespace std;

class Cylinder; // a forward declaration

enum colors { red, green, yellow };

class Cube {
colors color;
public:
Cube(colors c) { color = c; }
friend bool sameColor(Cube x, Cylinder y);
};

class Cylinder {
colors color;
public:
Cylinder(colors c) { color= c; }
friend bool sameColor(Cube x, Cylinder y);
};

bool sameColor(Cube x, Cylinder y)
{
if(x.color == y.color)
return true;
else
return false;
}

int main()
{
Cube cube1(red);
Cube cube2(green);
Cylinder cyl(green);

if(sameColor(cube1, cyl))
cout << "cube1 and cyl are the same color.\n";
else
cout << "cube1 and cyl are different colors.\n";

if(sameColor(cube2, cyl))
cout << "cube2 and cyl are the same color.\n";
else
cout << "cube2 and cyl are different colors.\n";

return 0;
}</source>
<pre class=codeResult>cube1 and cyl are different colors.
cube2 and cyl are the same color.</pre>

==friend square() function for Distance==

<source lang="cpp">#include <iostream>
using namespace std;
class Distance{
private:
int feet;
float inches;
public:
Distance() : feet(0), inches(0.0){ }

Distance(int ft, float in) : feet(ft), inches(in){ }
void showdist(){
cout << feet << "\"-" << inches << "\"";
}
friend float square(Distance);
};
float square(Distance d){
float fltfeet = d.feet + d.inches/12;
float feetsqrd = fltfeet * fltfeet;
return feetsqrd;
}
int main(){
Distance dist(3, 6.0);
float sqft;

sqft = square(dist);
dist.showdist();
cout << sqft;
return 0;
}</source>

==Share friend function between classes==

<source lang="cpp">#include<iostream.h>
class MyClassB;
class MyClassA
{
char *name;
public:
MyClassA(char *s){name=s;}
friend void print(MyClassA &,MyClassB &);
};
class MyClassB
{
char *name;
public:
MyClassB(char *s){name=s;}
friend void print(MyClassA &,MyClassB &);
};
void print(MyClassA &a,MyClassB &b)
{
cout<<"the MyClassA is"<<a.name<<endl;
cout<<"the MyClassB is"<<b.name<<endl;
}
int main()
{
MyClassA s("Li Hu");
MyClassB t("Wan Ping");
print(s,t);
}</source>
<pre class=codeResult>the MyClassA isLi Hu
the MyClassB isWan Ping</pre>

← Предыдущая	Версия 14:21, 25 мая 2010
(нет различий)

C++ Tutorial/Class/friend function - История изменений

в 14:21, 25 мая 2010

Admin: 1 версия: Импорт контента...