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C++ Tutorial - Lesson 15: Function Overloading

Function Overloading, Page 1

by John Kopp

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Welcome to EasyCPlusPlus.com's free tutorial on C++ programming. This lesson covers overloaded functions. Function overloading provides a way to have multiple functions with the same name. Why would this be of benefit? Let's look at a simple example. Suppose it's needed to have a function that converts a temperature from Fahrenheit to Celsius.

Prototype (Declaration):

void ConvertFToC(float f, float &c);

Definition:

void ConvertFToC(float f, float &c)
{
    c = (f - 32.) * 5./9.;
}

Now suppose that a Convert function is also needed to convert an integer Fahrenheit temperature to Celsius in the same program. One approach would be to give this function a new name, and perhaps to update the name of the "float" version as well.

void fConvertFToC(float f, float &c);
void iConvertFToC(int f, int &c);

That's not too bad. There are only two function names to keep track off. Now suppose that a higher precision, double, version is needed, or a version for data type short or long.

void fConvertFToC(float f, float &c);
void iConvertFToC(int f, int &c);
void dConvertFToC(double f, double &c);
void lConvertFToC(long f, long &c);
void sConvertFToC(short f, short &c);

As can be seen, this is quickly becoming a lexical nightmare. It is now necessary to remember five different function names for functions that essentially perform the same calculation. Someone reading or maintaining a program using these functions is bound to become quickly confused. It is not clear that exactly how exactly how each differs. Are only the data types different or are there differences in calculation? Fortunately, function overloading provides an alternative. The same function name can be used for multiple functions provided each differs in the number or type of its parameters. For each call of the function, the compiler compares the number and type of the arguments in the call against the parameter lists of each version of the function. The compiler selects the appropriate version. This process is call function resolution.

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