When working with legacy C++ code, it’s not uncommon to encounter code that is difficult to understand, maintain, or extend. These codebases often suffer from what is known as “code smells” - symptoms of poor design or implementation choices. Identifying and addressing these smells can greatly improve the quality and maintainability of the code.

In this article, we’ll explore some common code smells that you can look out for in legacy C++ code.

1. Long Methods

Long methods are a clear indication of code complexity. When a method is too long, it becomes harder to understand and can result in code duplication and maintainability issues. Look out for methods that contain a large number of lines or perform multiple different tasks.

Example:

void processOrder(Order& order) {
    // ... 100 lines of code ...
    // ... multiple conditional statements ...
    // ... complex algorithm ...
    // ... 100 more lines of code ...
}

2. Large Classes

Similar to long methods, large classes are another sign of code complexity. A class that does too many things violates the Single Responsibility Principle (SRP) and makes the code harder to understand and maintain. Look for classes that have too many member variables and methods.

Example:

class Customer {
    // ... 10 member variables ...
    // ... 20 member functions ...
};

3. Deeply Nested Control Flow

Deeply nested if-else statements or switch-case blocks can be challenging to comprehend and debug. They often indicate complex conditional logic or tight coupling between components. Aim for a shallow control flow hierarchy by extracting complex conditions into separate methods or objects.

Example:

if (condition1) {
    if (condition2) {
        if (condition3) {
            // ... nested code ...
        } else {
            // ... nested code ...
        }
    } else {
        // ... nested code ...
    }
} else {
    // ... nested code ...
}

4. Excessive Comments or Code Duplication

While comments are essential for documenting code, excessive comments can indicate a lack of clear and concise code. Similarly, code duplication is a sign of poor code reuse and can lead to maintenance challenges. Look for places where code could be refactored to eliminate duplication or unnecessary comments.

Example:

// Compute the area of a rectangle
int area(int width, int height) {
    // Multiply width by height to get the area
    return width * height;
}

5. Lack of Unit Tests

Legacy codebases often lack proper unit tests, making it difficult to refactor or modify the code without introducing bugs. A lack of tests can also make it harder to understand the intended behavior of the code. Identify areas where tests are missing and consider adding them before making any changes.

Conclusion

Identifying code smells is the first step towards improving legacy C++ codebases. By being aware of common code smells such as long methods, large classes, deeply nested control flow, excessive comments or code duplication, and lack of unit tests, you can start to refactor and improve the quality of your code.

Remember, it’s essential to approach code refactoring with caution, making small incremental changes while ensuring proper testing to avoid introducing new bugs.