C++/Overload/Inserter
Содержание
An inserter can be used to output data in any form
#include <iostream>
using namespace std;
class MyClass {
int x, y;
public:
MyClass(int i, int j) {
x=i;
y=j;
}
friend ostream &operator<<(ostream &stream, MyClass o);
};
ostream &operator<<(ostream &stream, MyClass o)
{
register int i, j;
for(i=0; i<o.x; i++)
stream << "*";
stream << "\n";
for(j=1; j<o.y-1; j++) {
for(i=0; i<o.x; i++)
if(i==0 || i==o.x-1) stream << "*";
else stream << " ";
stream << "\n";
}
for(i=0; i<o.x; i++)
stream << "*";
stream << "\n";
return stream;
}
int main()
{
MyClass a(14, 6), b(30, 7), c(40, 5);
cout << "Here are some:\n";
cout << a << b << c;
return 0;
}
Create a non-friend inserter.
#include <iostream>
using namespace std;
class MyClass {
public:
int x, y; // must be public
MyClass() {
x = 0;
y = 0;
}
MyClass(int i, int j) {
x = i;
y = j;
}
};
// An inserter for the MyClass class.
ostream &operator<<(ostream &stream, MyClass ob)
{
stream << ob.x << ", " << ob.y << "\n";
return stream;
}
int main()
{
MyClass a(1, 1), b(10, 23);
cout << a << b;
return 0;
}
Output account info to a file using an inserter.
#include <iostream>
#include <fstream>
#include <cstring>
using namespace std;
class account {
int custnum;
char name[80];
double balance;
public:
account(int c, char *n, double b)
{
custnum = c;
strcpy(name, n);
balance = b;
}
friend ostream &operator<<(ostream &stream, account ob);
};
ostream &operator<<(ostream &stream, account ob)
{
stream << ob.custnum << " ";
stream << ob.name << " " << ob.balance;
stream << "\n";
return stream;
}
int main()
{
account Rex(1011, "Joe", 12323.34);
ofstream out("accounts", ios::out | ios::binary);
if(!out) {
cout << "Cannot open output file.\n";
return 1;
}
out << Rex;
out.close();
return 0;
}
PhoneNumber inserter function
#include <iostream>
#include <cstring>
using namespace std;
class PhoneNumber {
public:
char name[80];
int areaCode;
int prefix;
int num;
PhoneNumber(char *n, int a, int p, int nm){
strcpy(name, n);
areaCode = a;
prefix = p;
num = nm;
}
};
// Display name and phone number.
ostream &operator<<(ostream &stream, PhoneNumber o)
{
stream << o.name << " ";
stream << "(" << o.areaCode << ") ";
stream << o.prefix << "-" << o.num << "\n";
return stream; // must return stream
}
int main()
{
PhoneNumber a("T", 111, 555, 1234);
PhoneNumber b("A", 312, 555, 5768);
PhoneNumber c("T", 212, 555, 9991);
cout << a << b << c;
return 0;
}
This program draws right triangles
#include <iostream>
using namespace std;
class triangle {
int height, base;
public:
triangle(int h, int b) { height = h; base = b; }
friend ostream &operator<<(ostream &stream, triangle ob);
};
// Draw a triangle.
ostream &operator<<(ostream &stream, triangle ob)
{
int i, j, h, k;
i = j = ob.base-1;
for(h=ob.height-1; h; h--) {
for(k=i; k; k--)
stream << " ";
stream << "*";
if(j!=i) {
for(k=j-i-1; k; k--)
stream << " ";
stream << "*";
}
i--;
stream << "\n";
}
for(k=0; k<ob.base; k++) stream << "*";
stream << "\n";
return stream;
}
int main()
{
triangle t1(5, 5), t2(10, 10), t3(12, 12);
cout << t1;
cout << endl << t2 << endl << t3;
return 0;
}
Use a friend inserter for objects of type MyClass.
#include <iostream>
using namespace std;
class MyClass {
int x, y;
public:
MyClass() {
x = 0;
y = 0;
}
MyClass(int i, int j) {
x = i;
y = j;
}
friend ostream &operator<<(ostream &stream, MyClass ob);
};
ostream &operator<<(ostream &stream, MyClass ob)
{
stream << ob.x << ", " << ob.y << "\n";
return stream;
}
int main()
{
MyClass a(1, 1), b(10, 23);
cout << a << b;
return 0;
}
Use friend function to operator: <<, >>
>" src="http://www.java2s.com/Code/CppImages/Usefriendfunctiontooperator.PNG">
#include <iostream>
using namespace std;
class factor {
int num; // number
int lfact; // lowest factor
public:
factor(int i);
friend ostream &operator<<(ostream &stream, factor ob);
friend istream &operator>>(istream &stream, factor &ob);
};
factor::factor(int i)
{
int n;
num = i;
for(n=2; n < (i/2); n++)
if(!(i%n)) break;
if(n<(i/2)) lfact = n;
else lfact = 1;
}
istream &operator>>(istream &stream, factor &ob)
{
stream >> ob.num;
int n;
for(n=2; n < (ob.num/2); n++)
if(!(ob.num%n)) break;
if(n < (ob.num/2))
ob.lfact = n;
else
ob.lfact = 1;
return stream;
}
ostream &operator<<(ostream &stream, factor ob)
{
stream << ob.lfact << " is lowest factor of ";
stream << ob.num << "\n";
return stream;
}
int main()
{
factor o(32);
cout << o;
cin >> o;
cout << o;
return 0;
}
