C++ Tutorial/Operator Overloading/overload ostream istream operator
Содержание
- 1 Class level ostream operator and istream operator
- 2 Class ostream operator
- 3 Complex logic in ostream operator
- 4 friend ostream operator for private fields
- 5 Ignore: manipulator that ignores N lines
- 6 istream operator with data check
- 7 ostream and istream operator for a class
- 8 Overloading >>: To demonstrate a custom inserter, one will be created for objects of type phonebook, shown here.
- 9 Overload
- 10 Overload ostream and istream operator
Class level ostream operator and istream operator
<source lang="cpp">#include<iostream.h>
- include<fstream.h>
class ThreeD {
int x,y,z;
public:
ThreeD(int i,int j,int k){
x=i;
y=j;
z=k;
}
friend ostream& operator<<(ostream& stream,ThreeD ob);
friend istream& operator>>(istream& stream,ThreeD ob);
}; ostream& operator<<(ostream& stream,ThreeD ob) {
stream<<ob.x<<" "<<ob.y<<" "<<ob.z<<"\n"; return stream;
} istream& operator>>(istream& stream,ThreeD ob) {
stream>>ob.x>>ob.y>>ob.z; return stream;
} main() {
ThreeD o1(1,2,3),o2(4,5,6);
ofstream out("test");
if(!out)
{
cout<<"Cannot open output file\n";
return 1;
}
cout<<o1<<o2;
out.close();
ifstream in("test");
if(!in)
{
cout<<"Cannot open input file\n";
return 1;
}
ThreeD o3(0,0,0),o4(0,0,0);
in>>o3>>o4;
return 0;
}</source>
1 2 3 4 5 6
Class ostream operator
<source lang="cpp">#include <iostream>
- include <cstring>
using namespace std; class MyClass { public:
char name[80];
int areacode;
int prefix;
int num;
MyClass(char *n, int a, int p, int nm)
{
strcpy(name, n);
areacode = a;
prefix = p;
num = nm;
}
}; ostream &operator<<(ostream &stream, MyClass o) {
stream << o.name << " ";
stream << "(" << o.areacode << ") ";
stream << o.prefix << "-" << o.num << "\n";
return stream;
} int main() {
MyClass a("T", 1, 5, 1);
MyClass b("A", 3, 5, 5);
MyClass c("T", 2, 5, 9);
cout << a << b << c;
return 0;
}</source>
T (1) 5-1 A (3) 5-5 T (2) 5-9
Complex logic in ostream operator
<source lang="cpp">#include <iostream> using namespace std; class Line {
int x;
public:
Line(int i) { x=i; }
friend ostream &operator<<(ostream &stream, Line o);
}; ostream &operator<<(ostream &stream, Line o) {
register int i, j;
for(i=0; i<o.x; i++)
stream << "*";
stream << "\n";
return stream;
} int main() {
Line a(14), b(30), c(40); cout << a << b << c; return 0;
}</source>
************** ****************************** ****************************************
friend ostream operator for private fields
<source lang="cpp">#include <iostream>
- include <cstring>
using namespace std; class MyClass {
// now private char name[80]; int areacode; int prefix; int num;
public:
MyClass(char *n, int a, int p, int nm)
{
strcpy(name, n);
areacode = a;
prefix = p;
num = nm;
}
friend ostream &operator<<(ostream &stream, MyClass o);
}; ostream &operator<<(ostream &stream, MyClass o) {
stream << o.name << " ";
stream << "(" << o.areacode << ") ";
stream << o.prefix << "-" << o.num << "\n";
return stream;
} int main() {
MyClass a("T", 1, 5, 1);
MyClass b("A", 3, 5, 5);
MyClass c("T", 2, 5, 9);
cout << a << b << c;
return 0;
}</source>
T (1) 5-1 A (3) 5-5 T (2) 5-9
Ignore: manipulator that ignores N lines
<source lang="cpp">/* The following code example is taken from the book
* "The C++ Standard Library - A Tutorial and Reference" * by Nicolai M. Josuttis, Addison-Wesley, 1999 * * (C) Copyright Nicolai M. Josuttis 1999. * 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>
- include <limits>
// Ignore: manipulator that ignores N lines class Ignore {
public:
int num;
Ignore(int n) : num(n) {
}
}; // convenience function Ignore ignore(int n) {
return Ignore(n);
} std::istream& operator >> (std::istream& strm, const Ignore& manip) {
for (int i=0; i<manip.num; ++i) {
strm.ignore(std::numeric_limits<int>::max(),"\n");
}
return strm;
}
int main() {
char c; std::cout << "ignore two lines and print frist character following them\n"; std::cin >> ignore(2) >> c; std::cout << "c: " << c << std::endl;
}</source>
ignore two lines and print frist character following them a v a c: a
istream operator with data check
<source lang="cpp">#include<iostream.h> class Time {
int hour; int minute; int second;
public:
friend ostream& operator<<( ostream &, Time); friend istream& operator>>( istream &,Time &);
}; ostream& operator<<( ostream & out, Time t) {
out<<"\nHere"s the time:\n"; out<<t.hour<<":"<<t.minute<<":"<<t.second<<"\n"; return out;
} istream& operator>>( istream & in ,Time & t) {
cout<<"Please enter the time as follow\n";
do{
cout<<"What is the hour(0-23)?";
in>>t.hour;
if((t.hour<0)||(t.hour>23))
cout<<"You have inpitted a wrong data! Please try again!\n";
}while((t.hour<0)||(t.hour>23));
do{
cout<<"What is the minute(0-59)?";
in>>t.minute;
if((t.minute<0)||(t.minute>59))
cout<<"You have inpitted a wrong data! Please try again!\n";
}while((t.minute<0)||(t.minute>59));
do{
cout<<"What is the second(0-23)?";
in>>t.second;
if((t.second<0)||(t.second>59))
cout<<"You have inpitted a wrong data! Please try again!\n";
}while((t.second<0)||(t.second>59));
return in;
} main() {
Time now; cin>>now; cout<<now; return 0;
}</source>
Please enter the time as follow What is the hour(0-23)?12 What is the minute(0-59)?12 What is the second(0-23)?12 Here"s the time: 12:12:12
ostream and istream operator for a class
<source lang="cpp">#include <iostream>
- include <cstring>
using namespace std; class MyClass {
char name[80]; int id; int prefix; int value;
public:
MyClass() { };
MyClass(char *n, int a, int p, int nm)
{
strcpy(name, n);
id = a;
prefix = p;
value = nm;
}
friend ostream &operator<<(ostream &stream, MyClass o);
friend istream &operator>>(istream &stream, MyClass &o);
}; // Display name and phone valueber. ostream &operator<<(ostream &stream, MyClass o) {
stream << o.name << " ";
stream << "(" << o.id << ") ";
stream << o.prefix << "-" << o.value << "\n";
return stream; // must return stream
} // Input name and telephone valueber. istream &operator>>(istream &stream, MyClass &o) {
cout << "Enter name: "; stream >> o.name; cout << "Enter id: "; stream >> o.id; cout << "Enter prefix: "; stream >> o.prefix; cout << "Enter value: "; stream >> o.value; cout << "\n"; return stream;
} int main() {
MyClass a; cin >> a; cout << a; return 0;
}</source>
Enter name: Joe Enter id: 123 Enter prefix: 1 Enter value: 2 Joe (123) 1-2
Overloading >>: To demonstrate a custom inserter, one will be created for objects of type phonebook, shown here.
<source lang="cpp">#include <iostream>
- include <cstring>
using namespace std;
class phonebook { public:
char name[80];
int areacode;
int prefix;
int num;
phonebook(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, phonebook o) {
stream << o.name << " ";
stream << "(" << o.areacode << ") ";
stream << o.prefix << "-" << o.num << "\n";
return stream; // must return stream
}
int main() {
phonebook a("A", 111, 555, 1234);
phonebook b("B", 312, 555, 5768);
phonebook c("C", 212, 555, 9991);
cout << a << b << c;
return 0;
}</source>
Overload
<source lang="cpp">#include <iostream>
- include <cstring>
using namespace std;
class phonebook {
// now private char name[80]; int areacode; int prefix; int num;
public:
phonebook(char *n, int a, int p, int nm)
{
strcpy(name, n);
areacode = a;
prefix = p;
num = nm;
}
friend ostream &operator<<(ostream &stream, phonebook o);
};
// Display name and phone number. ostream &operator<<(ostream &stream, phonebook o) {
stream << o.name << " ";
stream << "(" << o.areacode << ") ";
stream << o.prefix << "-" << o.num << "\n";
return stream; // must return stream
}
int main() {
phonebook a("A", 111, 555, 1234);
phonebook b("B", 312, 555, 5768);
phonebook c("C", 212, 555, 9991);
cout << a << b << c;
return 0;
}</source>
Overload ostream and istream operator
<source lang="cpp">#include <iostream>
- include <fstream>
- include <cstring>
using namespace std; class MyClass {
char name[80]; char areacode[4]; char prefix[4]; char num[5];
public:
MyClass() { };
MyClass(char *n, char *a, char *p, char *nm)
{
strcpy(name, n);
strcpy(areacode, a);
strcpy(prefix, p);
strcpy(num, nm);
}
friend ostream &operator<<(ostream &stream, MyClass o);
friend istream &operator>>(istream &stream, MyClass &o);
}; // Display name and phone number. ostream &operator<<(ostream &stream, MyClass o) {
stream << o.name << " ";
stream << "(" << o.areacode << ") ";
stream << o.prefix << "-";
stream << o.num << "\n";
return stream; // must return stream
} // Input name and telephone number. istream &operator>>(istream &stream, MyClass &o) {
cout << "Enter name: "; stream >> o.name; cout << "Enter area code: "; stream >> o.areacode; cout << "Enter prefix: "; stream >> o.prefix; cout << "Enter number: "; stream >> o.num; cout << "\n"; return stream;
} int main() {
MyClass a;
char c;
fstream pb("phone", ios::in | ios::out | ios::app);
if(!pb) {
cout << "Cannot open phone book file.\n";
return 1;
}
cin >> a;
pb << a; // write to disk
char ch;
pb.seekg(0, ios::beg);
while(!pb.eof()) {
pb.get(ch);
if(!pb.eof()) cout << ch;
}
pb.clear(); // reset eof
cout << endl;
pb.close();
}</source>
Cannot open phone book file.
