1. COP 3330 Object-oriented Programming in C++
Template
Spring 2019

2. Function Template
A function template can perform the same algorithm for different types without specifying the types in advance
Example: a function that computes the maximum for three different integers
int maximum(int a, int b, int c) {
int max = a;
if (b > max) max = b;
if (c > max) max = c;
return max; }

3. Function Template
However, this function only works for int variables (or types that can be automatically converted to int)
What if we wanted to compare variables with the type double?
Do we have to write a new function?
A function template allows this problem to be solved easily, with only one function

4. Function Template
template<class T> T maximum(T value1, T value2, T value3) { T maximumValue = value1; if (value2 > maximumValue) maximumValue = value2; if (value3 > maximumvalue) maximumValue = value3; return maximumValue; }

5. How to Use?
int main() { int int1, int2, int3; cout << “Input three integer values: “; cin >> int1 >> int2 >> int3; cout << “The maximum integer value is: “; << maximum(int1, int2, int3); double double1, double2, double3; cout << “\n\nInput three double values: “; cin >> double1 >> double2 >> double3; cout << “The maximum double value is: “; << maximum(double1, double2, double3); char char1, char2, char3; cout << “\n\nInput three characters: “; cin >> char1 >> char2 >> char3; cout << “The maximum character value is: “ << maximum(char1, char2, char3); return 0; }

6. Another Example
This is a function template that prints the contents of the array
template<class T>
void printArray(const T*array, const int count) {
for (int j = 0; j < count; j++)
cout << array[j] << “ “;
cout << endl; }
This function will work on arrays of ANY class type when an appropriate insertion operator << has been overloaded

7. How to Use?
int main() { const int aCount = 5; const int bCount = 7; const int cCount = 6; int a[aCount] = {1, 2, 3, 4, 5}; double b[bCount] = {1.1, 2.2, 3.3, 4.4, 5.5, 6.6, 7.7}; char c[cCount] = “HELLO”; cout << “Array a contains: “ << endl; printArray(a, aCount); cout << “Array b contains: “ << endl; printArray(b, bCount); cout << “Array c contains: “ << endl; printArray(c, cCount); return 0; }

8. Class Template
Suppose we want to design a class that uses array-bases storage to maintain a list of integers
With class templates, we can make this class work with different types without altering and recompiling code
To make a class into a template, prefix the class definition with the syntax
template<class T>
T is a type parameter, and it can have ANY name
When the class is instantiated, we fill in an appropriate type
Use the same prefix on the definitions of the member functions

9. Class Template For member functions, the name of the class will be
className<T>::functionName
Also, in the main program, we must #include the actual definition file, in addition to the class declaration
The compiler creates a different version of the class for each type that is used
Thus, either the entire class should be written in the header file, OR the .cpp file should be included
#include “templatelist.cpp”

10. Code Review

11. Questions