ece 462 object-oriented programming using c++ and java ... · yhl operator overloading 4 binary...

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ECE 462Object-Oriented Programming

using C++ and Java

Operator Overloading in C++

Yung-Hsiang Luyunglu@purdue.edu

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Operator Overloading in C++

You have been using overloaded operators for years.• 3 + 5 // integer addition (bit-wise + carries)• 3.5 + 0.0059 // floating point addition

// 1. align the decimal points// 2. add significands// 3. normalized and update exponent

• “hello” + “ world” // intuitively, it means append• Operator overloading is not essential in object-oriented

programming. In fact, Java does not allow programmer-defined operator overloading.

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Overloading Operators in C++

• We have seen overloaded operator for << >> and =• at least one operand (for binary operators) must be an

object or enumeration type (i.e. not a built-in type)• precedence not changed• arity not changed (! always unary)• argument(s) may be passed by value (copy) or by

reference, not by pointer• default argument value(s) illegal• cannot overload :: .* . ?:

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Binary Operators

• If the first operand is an object, a binary operator can be implemented in two forms– a member function, the first operand is this object– a “free” function (not a member of any class), usually

declared as a friend to access private attributes – not both

• If the first operand is not an object (such as int), the operator must be a free function.

• In most cases, the operand object(s) should use reference to prevent calling copy constructor.

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Global Function(not a member function of a class)

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Copy Constructor and Operator Overloading

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Member Function(first operand is "this")

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binary operator withonly one parameter

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Binary Operator, One Input?

first + second;

can be thought of asfirst.operator + (second);

This operator is a member function. Hence, the first operand is given by the first object.

cout << first;

can be thought of ascout.operator << (first);

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Unary Operator, Global Function

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unary operator withonly one parameter

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Unary Operator, Member Function

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unary operator without parameter ("this" is the parameter)

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Comparison Operator <

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Equality Operator ==

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Self Test

YHL Small Int 1

ECE 462Object-Oriented Programming

using C++ and Java

Small Int and Conversion

Yung-Hsiang Luyunglu@purdue.edu

YHL Small Int 2

Increment and Decrement Operators (Small Int)

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//prefix increment operator, such as ++iinline SmallInt& SmallInt::operator++() {

if (value < MAX) { value ++; } else { cerr << "Error: Range of SmallInt violated" << endl; }return *this;

}

//postfix increment operator, , such as i++inline const SmallInt SmallInt::operator++(int) {

SmallInt oldValue = *this;++(*this); // call the prefix increment operatorreturn oldValue;

}

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prefix and postfix increment

void f1(int i) {cout << i << endl;

}int x = 5;f1(++x); // increment before calling f1, outupt 6cout << x << endl; // 6f1(x ++); // increment after calling f1, output 6cout << x << endl; // 7

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inline

• inline ⇒ suggest C++ compiler to replace the function call by the function body to reduce the call overhead

• function call overhead– push the current location to the call stack– push the parameters' values to the call stack– change the program counter to the called function's address– execute the code in the function // useful work– pop the stack to get the return address– change the program counter to the return address

• inline replaces the call by the code inside the function

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Programmer Defined(Implicit) Class Conversion

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Explicit in C++

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Self Test