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C + + : T h e C o m p l e t e R e f e r e n c e functions in the following example program. These functions could not be replaced by a generic function because they do not do the same thing.
#include <iostream>
#include <cmath> using namespace std; void myfunc(int i)
{ cout << "value is: " << i << "\n";
} void myfunc(double d)
{ double intpart; double fracpart;
} fracpart = modf(d, &intpart); cout << "Fractional part: " << fracpart; cout << "\n"; cout << "Integer part: " << intpart; int main()
{ myfunc(1); myfunc(12.2);
} return 0;
Applying Generic Functions
Generic functions are one of C++'s most useful features. They can be applied to all types of situations. As mentioned earlier, whenever you have a function that defines a generalizable algorithm, you can make it into a template function. Once you have done so, you may use it with any type of data without having to recode it. Before moving on to generic classes, two examples of applying generic functions will be given. They illustrate how easy it is to take advantage of this powerful C++ feature.
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A Generic Sort
Sorting is exactly the type of operation for which generic functions were designed.
Within wide latitude, a sorting algorithm is the same no matter what type of data is being sorted. The following program illustrates this by creating a generic bubble sort.
While the bubble sort is a rather poor sorting algorithm, its operation is clear and uncluttered and it makes an easy-to-understand example. The bubble( ) function will sort any type of array. It is called with a pointer to the first element in the array and the number of elements in the array.
// A Generic bubble sort.
#include <iostream> using namespace std; template <class X> void bubble(
X *items, // pointer to array to be sorted int count) // number of items in array
{ register int a, b;
X t;
} for(a=1; a<count; a++) for(b=count-1; b>=a; b--) if(items[b-1] > items[b]) {
// exchange elements t = items[b-1]; items[b-1] = items[b]; items[b] = t;
} int main()
{ int iarray[7] = {7, 5, 4, 3, 9, 8, 6}; double darray[5] = {4.3, 2.5, -0.9, 100.2, 3.0}; int i; cout << "Here is unsorted integer array: "; for(i=0; i<7; i++)
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C + + : T h e C o m p l e t e R e f e r e n c e cout << iarray[i] << ' '; cout << endl; cout << "Here is unsorted double array: "; for(i=0; i<5; i++) cout << darray[i] << ' '; cout << endl; bubble(iarray, 7); bubble(darray, 5); cout << "Here is sorted integer array: "; for(i=0; i<7; i++) cout << iarray[i] << ' '; cout << endl; cout << "Here is sorted double array: "; for(i=0; i<5; i++) cout << darray[i] << ' '; cout << endl;
} return 0;
The output produced by the program is shown here.
Here is unsorted integer array: 7 5 4 3 9 8 6
Here is unsorted double array: 4.3 2.5 -0.9 100.2 3
Here is sorted integer array: 3 4 5 6 7 8 9
Here is sorted double array: -0.9 2.5 3 4.3 100.2
As you can see, the preceding program creates two arrays: one integer and one double.
It then sorts each. Because bubble( ) is a template function, it is automatically overloaded to accommodate the two different types of data. You might want to try using
bubble( )
to sort other types of data, including classes that you create. In each case, the compiler will create the right version of the function for you.
Compacting an Array
Another function that benefits from being made into a template is called compact( ).
This function compacts the elements in an array. It is not uncommon to want to remove elements from the middle of an array and then move the remaining elements down so
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471 that all unused elements are at the end. This sort of operation is the same for all types of arrays because it is independent of the type data actually being operated upon. The generic compact( ) function shown in the following program is called with a pointer to the first element in the array, the number of elements in the array, and the starting and ending indexes of the elements to be removed. The function then removes those elements and compacts the array. For the purposes of illustration, it also zeroes the unused elements at the end of the array that have been freed by the compaction.
// A Generic array compaction function.
#include <iostream> using namespace std; template <class X> void compact(
X *items, // pointer to array to be compacted int count, // number of items in array int start, // starting index of compacted region int end) // ending index of compacted region
{ register int i; for(i=end+1; i<count; i++, start++) items[start] = items[i];
}
/* For the sake of illustration, the remainder of the array will be zeroed. */ for( ; start<count; start++) items[start] = (X) 0; int main()
{ int nums[7] = {0, 1, 2, 3, 4, 5, 6}; char str[18] = "Generic Functions"; int i; cout << "Here is uncompacted integer array: "; for(i=0; i<7; i++) cout << nums[i] << ' '; cout << endl; cout << "Here is uncompacted string: "; for(i=0; i<18; i++)
