Cyclomatic complexity

Cyclomatic complexity is a quantitative measure of a program’s structural complexity. It is a measure of the number of linearly independent paths through a program’s (or component’s) source code.

A linear sequence of statements with no branching has a cyclomatic complexity of 1, and each conditional (an if or a while, for example) adds one further path. So the metric roughly tracks the count of conditional statements in the code, plus one.

The metric, introduced by Thomas McCabe in 1976, is widely used as a proxy for how hard a function or module is to understand and test, since each independent path is a case that has to be reasoned about and, ideally, covered by a test. Many software engineers hold that higher cyclomatic complexity correlates with a higher defect rate, and teams often set a threshold above which a function is flagged for refactoring.

References

• McCabe, TJ (1976). A Complexity Measure. IEEE Transactions on Software Engineering, SE-2(4).