Duplicate code
Duplicate code is a computer programming term for a sequence of code that occurs more than once in a programs source code. A minimum requirement is usually applied to the quantity of code that must appear in a sequence for it to be considered a duplicate rather than a coincidental similarity.
Sequences of duplicate code are sometimes known as clones.
The following are some of the ways in which two code sequences can be a duplicate of each other:
- character for character identical
- character for character identical with white space characters and comments being ignored
- token for token identical
- functionally identical
A number of different algorithms have been proposed to detect duplicate code:
- Baker's paper
- Swiss work on visual clone detection
- other people
Example of functionally duplicate code
Consider the following code snippit for caluclating the average of an array of integers
int array1[4] = {3,5,7,9}
int array2[3] = {2,4,6]
int sum1 = 0;
int sum2 = 0;
int average1 = 0;
int average2 = 0;
for (int i = 0; i < 4; i++)
{
sum1 += array1[i];
}
average1 = sum1/4;
for (int i = 0; i < 3; i++)
{
sum2 += array2[i];
}
average2 = sum1/3;
The two functions can be rewritten as the single function:
int calcAverage (int* myArray, int length)
{
int sum = 0;
for (int i = 0; i < length; i++)
{
sum += myArray[i];
}
return sum/length;
}