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Непонятный вывод: постфиксные и префиксные инкремент/декремент
27.08.2013, 12:29. Показов 876. Ответов 2
Под спойлером весь который можно просто скопипастить и запустить в онлайн компиляторе http://www.compileonline.com/c... online.php
Кликните здесь для просмотра всего текста
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| #include <iostream>
using namespace std;
//-------------------------------------------------------
// class Int
class Int {
public:
// constructors
Int(int n = 0) : member(n) { }
Int(const Int& i) : member(i.member) { }
Int& operator=(const Int& i);
// access
int data() const { return member; }
// modyfication
void set_member(int n) { member = n; }
// operators
const Int& operator+() {return *this; } // unary+ operator
const Int operator-() {return Int(-this->member); } //unary- operator
const Int& operator++() {++member; return *this; } // prefix ++ increment operator
const Int operator++(int) {Int Old_value(*this); ++member; return Old_value; } // postfix ++ increment operator
const Int& operator--() {--member; return *this; } // prefix ++ increment operator
const Int operator--(int) {Int Old_value(*this); --member; return Old_value; } // postfix ++ increment operator
private:
int member;
};
//-------------------
// members
// assignment operator
Int& Int::operator=(const Int& i) {
if(this==&i) return *this;
member = i.member;
return *this;
}
//-------------------
// not members
// binary operator+
const Int operator+(const Int& left, const Int& right) {
return Int(left.data()+right.data());
}
//-------------------
// binary operator-
const Int operator-(const Int& left, const Int& right) {
return Int(left.data()-right.data());
}
//-------------------
// binary operator*
const Int operator*(const Int& left, const Int& right) {
return Int(left.data()*right.data());
}
//-------------------
// binary operator/
const Int operator/(const Int& left, const Int& right) {
return Int(left.data()/right.data());
}
//-------------------
// binary operator%
const Int operator%(const Int& left, const Int& right) {
return Int(left.data()%right.data());
}
//-------------------
// operator>>
istream& operator>>(istream& is, Int& i) {
int n;
is >> n;
if (is) i.set_member(n);
return is;
}
//-------------------
// operator<<
ostream& operator<<(ostream& os, const Int& i) {
os << i.data();
return os;
}
//-------------------------------------------------------
// class template<class T> Number
template<class T>
class Number {
public:
// constructors
Number(T n = 0) : member(n) { }
Number(const Number& i) : member(i.member) { }
Number& operator=(const Number& n);
// access
T data() const { return member; }
// modyfication
void set_member(T n) { member = n; }
// operators
const Number& operator+() {return *this; } // unary+ operator
const Number operator-() {return Number(-member); } //unary- operator
const Number& operator++() {member++; return *this; } // prefix ++ increment operator
const Number operator++(int) {Number Old_value(*this); member++; return Old_value; } // postfix ++ increment operator
const Number& operator--() {member--; return *this; } // prefix ++ increment operator
const Number operator--(int) {Number Old_value(*this); member--; return Old_value; } // postfix ++ increment operator
private:
T member;
};
//-------------------
// members
// assignment operator
template<class T>
Number<T>& Number<T>::operator=(const Number<T>& n) {
if(this==&n) return *this;
member = n.member;
return *this;
}
//-------------------
// not members
// binary operator+
template<class T>
const Number<T> operator+(const Number<T>& left, const Number<T>& right) {
return Number<T>(left.data()+right.data());
}
//-------------------
// binary operator-
template<class T>
const Number<T> operator-(const Number<T>& left, const Number<T>& right) {
return Number<T>(left.data()-right.data());
}
//-------------------
// binary operator*
template<class T>
const Number<T> operator*(const Number<T>& left, const Number<T>& right) {
return Number<T>(left.data()*right.data());
}
//-------------------
// binary operator/
template<class T>
const Number<T> operator/(const Number<T>& left, const Number<T>& right) {
return Number<T>(left.data()/right.data());
}
//-------------------
// binary operator%
template<class T>
const Number<T> operator%(const Number<T>& left, const Number<T>& right) {
return Number<T>(left.data()%right.data());
}
//-------------------
// operator>>
template<class T>
istream& operator>>(istream& is, Number<T>& i) {
T n;
is >> n;
if (is) i.set_member(n);
return is;
}
//-------------------
// operator<<
template<class T>
ostream& operator<<(ostream& os, const Number<T>& i) {
os << i.data();
return os;
}
int main()
{
Int i(10);
cout << -i << "; and value is " << i << endl;
cout << --i << "; and value is " << i << endl;
cout << +i << "; and value is " << i << endl;
cout << ++i << "; and value is " << i << endl;
cout << "postfix operators" << endl;
cout << i++ << "; and value is " << i << endl;
cout << i-- << "; and value is " << i << endl;
cout << endl << "-----------------" << endl;
Number<int> n1(100);
Number<int> n2(5);
cout << n1 << " % " << n2 << " == " <<n1%n2 << endl;
cout << n1 << " / " << n2 << " == " <<n1/n2 << endl;
cout << n1 << " * " << n2 << " == " <<n1*n2 << endl;
cout << n1 << " - " << n2 << " == " <<n1-n2 << endl;
cout << n1 << " + " << n2 << " == " <<n1+n2 << endl;
cout << "n1 == 100; correct work:" << endl;
cout << n1;
cout << " prefix-- == " << --n1 << endl;
cout << n1;
cout << " postfix++ == " << n1++ << "; and n1 value == " << n1 << endl;
cout << "----------------" << endl;
cout << "n1 == 100; incorrect work:" << endl;
cout << n1 << " prefix-- == " << --n1 << endl;
cout << n1 << " postfix++ == " << n1++ << "; and n1 value == " << n1 << endl;
return 0;
} |
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Есть два класса.
Первый:
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| //-------------------------------------------------------
// class Int
class Int {
public:
// constructors
Int(int n = 0) : member(n) { }
Int(const Int& i) : member(i.member) { }
Int& operator=(const Int& i);
// access
int data() const { return member; }
// modyfication
void set_member(int n) { member = n; }
// operators
const Int& operator+() {return *this; } // unary+ operator
const Int operator-() {return Int(-this->member); } //unary- operator
const Int& operator++() {++member; return *this; } // prefix ++ increment operator
const Int operator++(int) {Int Old_value(*this); ++member; return Old_value; } // postfix ++ increment operator
const Int& operator--() {--member; return *this; } // prefix ++ increment operator
const Int operator--(int) {Int Old_value(*this); --member; return Old_value; } // postfix ++ increment operator
private:
int member;
};
//-------------------
// members
// assignment operator
Int& Int::operator=(const Int& i) {
if(this==&i) return *this;
member = i.member;
return *this;
}
//-------------------
// not members
// binary operator+
const Int operator+(const Int& left, const Int& right) {
return Int(left.data()+right.data());
}
//-------------------
// binary operator-
const Int operator-(const Int& left, const Int& right) {
return Int(left.data()-right.data());
}
//-------------------
// binary operator*
const Int operator*(const Int& left, const Int& right) {
return Int(left.data()*right.data());
}
//-------------------
// binary operator/
const Int operator/(const Int& left, const Int& right) {
return Int(left.data()/right.data());
}
//-------------------
// binary operator%
const Int operator%(const Int& left, const Int& right) {
return Int(left.data()%right.data());
}
//-------------------
// operator>>
istream& operator>>(istream& is, Int& i) {
int n;
is >> n;
if (is) i.set_member(n);
return is;
}
//-------------------
// operator<<
ostream& operator<<(ostream& os, const Int& i) {
os << i.data();
return os;
} |
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и второй (шаблонный класс на основе первого класса Int)
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| //-------------------------------------------------------
// class template<class T> Number
template<class T>
class Number {
public:
// constructors
Number(T n = 0) : member(n) { }
Number(const Number& i) : member(i.member) { }
Number& operator=(const Number& n);
// access
T data() const { return member; }
// modyfication
void set_member(T n) { member = n; }
// operators
const Number& operator+() {return *this; } // unary+ operator
const Number operator-() {return Number(-member); } //unary- operator
const Number& operator++() {member++; return *this; } // prefix ++ increment operator
const Number operator++(int) {Number Old_value(*this); member++; return Old_value; } // postfix ++ increment operator
const Number& operator--() {member--; return *this; } // prefix ++ increment operator
const Number operator--(int) {Number Old_value(*this); member--; return Old_value; } // postfix ++ increment operator
private:
T member;
};
//-------------------
// members
// assignment operator
template<class T>
Number<T>& Number<T>::operator=(const Number<T>& n) {
if(this==&n) return *this;
member = n.member;
return *this;
}
//-------------------
// not members
// binary operator+
template<class T>
const Number<T> operator+(const Number<T>& left, const Number<T>& right) {
return Number<T>(left.data()+right.data());
}
//-------------------
// binary operator-
template<class T>
const Number<T> operator-(const Number<T>& left, const Number<T>& right) {
return Number<T>(left.data()-right.data());
}
//-------------------
// binary operator*
template<class T>
const Number<T> operator*(const Number<T>& left, const Number<T>& right) {
return Number<T>(left.data()*right.data());
}
//-------------------
// binary operator/
template<class T>
const Number<T> operator/(const Number<T>& left, const Number<T>& right) {
return Number<T>(left.data()/right.data());
}
//-------------------
// binary operator%
template<class T>
const Number<T> operator%(const Number<T>& left, const Number<T>& right) {
return Number<T>(left.data()%right.data());
}
//-------------------
// operator>>
template<class T>
istream& operator>>(istream& is, Number<T>& i) {
T n;
is >> n;
if (is) i.set_member(n);
return is;
}
//-------------------
// operator<<
template<class T>
ostream& operator<<(ostream& os, const Number<T>& i) {
os << i.data();
return os;
} |
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Содержимое main()
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| int main()
{
Int i(10);
cout << -i << "; and value is " << i << endl;
cout << --i << "; and value is " << i << endl;
cout << +i << "; and value is " << i << endl;
cout << ++i << "; and value is " << i << endl;
cout << "postfix operators" << endl;
cout << i++ << "; and value is " << i << endl;
cout << i-- << "; and value is " << i << endl;
cout << endl << "-----------------" << endl;
Number<int> n1(100);
Number<int> n2(5);
cout << n1 << " % " << n2 << " == " <<n1%n2 << endl;
cout << n1 << " / " << n2 << " == " <<n1/n2 << endl;
cout << n1 << " * " << n2 << " == " <<n1*n2 << endl;
cout << n1 << " - " << n2 << " == " <<n1-n2 << endl;
cout << n1 << " + " << n2 << " == " <<n1+n2 << endl;
cout << "n1 == 100; correct work:" << endl;
cout << n1;
cout << " prefix-- == " << --n1 << endl;
cout << n1;
cout << " postfix++ == " << n1++ << "; and n1 value == " << n1 << endl;
cout << "----------------" << endl;
cout << "n1 == 100; incorrect work:" << endl;
cout << n1 << " prefix-- == " << --n1 << endl;
cout << n1 << " postfix++ == " << n1++ << "; and n1 value == " << n1 << endl;
return 0;
} |
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При выводе постфиксного и префиксного инкремента/декремента шаблонного класса Number используя поток cout и несколько операторов<<
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| cout << "n == 100; incorrect work:" << endl;
cout << n1 << " prefix-- == " << --n1 << endl;
cout << n1 << " postfix++ == " << n1++ << "; and n1 value == " << n1 << endl; |
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получаем несовсем то, что ожидалось.
Почему так?
Добавлено через 6 минут
Вывод:
correct work:
100 prefix-- == 99
99 postfix++ == 99; and n1 value == 100
----------------
incorrect work:
99 prefix-- == 99
100 postfix++ == 99; and n1 value == 100
0
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