Computer Science 1620

Function Overloading

Review Question: suppose I have the following function:

can I call this function with an integer?

yes – compiler will promote integer to double same thing applies to demotion

double square(double x) { return x * x;}

int main() { cout << square(3) << endl;

Function Overloading

Suppose you are in charge of writing a maximum function

The program must work with three different types: intdouble float

Function Overloading

First Way:

double maximum(double n1, double n2) {

if (n1 > n2)

return n1;

else

return n2;

}

Function Overloading

The previous example works fine, but inefficient consider following call

int x, y;

cin >> x >> y;

int z = maximum(x,y); consider what happens when compiling the program

the values x and y must be converted to type double in order to use the function

the return value is of type double … which must be converted back to an integer (which generates a compiler warning)

Function Overloading

Second Try:

int maximum(int n1, int n2) {

if (n1 > n2)

return n1;

else

return n2;

}

Function Overloading

The previous example works fine for integers, but what about doubles? consider following call

double x, y;

cin >> x >> y;

double z = maximum(x,y);

cout << z << endl; suppose I run this program, and type in the values 4.6 and 7.4 what will the output be?

Function Overloading

Second try:

double maximumDouble(double n1, double n2) { if (n1 > n2) return n1; else return n2;}

float maximumFloat(float n1, float n2) { if (n1 > n2) return n1; else return n2;}

int maximumInt(int n1, int n2) { if (n1 > n2) return n1; else return n2;}

Function Overloading

We can now change our original callint x, y;cin >> x >> y;int z = maximumInt(x,y);

no conversions take place some problems though

what if a programmer writes a program using integers … and the supervisor decides to use doubles instead

not only are you changing your variable types but now you have to change all of your calls to maximum

Function Overloading

Solution: Function overloadingC++ allows you to use the same function

name for different functions the functions must have different parameter

lists the function being called will depend on the

arguments being sent

Function Overloading

Last try:

double maximum(double n1, double n2) { if (n1 > n2) return n1; else return n2;}

float maximum(float n1, float n2) { if (n1 > n2) return n1; else return n2;}

int maximum(int n1, int n2) { if (n1 > n2) return n1; else return n2;}

Function Overloading

Now when we make the following call:int x, y;cin >> x >> y;int z = maximum(x,y);

no conversions take place

if we wanted to change to doubles, we need only change the variable type

double x, y;cin >> x >> y;double z = maximum(x,y);

Function Overloading

Resolving overloaded definitions the compiler must be able to choose

between two function declarationsalways chooses the best matchoverload resolution is a complex task

beyond scope of class

suffices to know that it tries for closest match