5 Common Software Bugs and How to Avoid Them (With Examples)

There are many reasons for bugs in software, such as oversights in testing processes, miscommunication, poor documentation, and time constraints. The thing about software bugs is that they can vary in severity and impact. While some bugs may be small and simple to address, others can result in major issues, such as system crashes, compromised security, data loss, and a negative user experience. To illustrate, so far in 2024, the global average cost of a data breach has reached $4.88 million, a 10% increase from the year before. Therefore, it is essential to detect and address bugs early in the software development lifecycle to ensure the delivery of high-quality software.

In this article, we break down the 5 most common software bugs and share some tips to help you prevent them to ensure the reliability and performance of your software products. 

1. Syntax errors

Syntax errors occur when the code structure does not match the programming language's rules. These errors prevent the program from being properly analyzed and lead to non-compliance. Typically, syntax errors are caught during the compilation or translation phase, before the program runs. They can be caused by a variety of issues such as:

• Missing or misplaced punctuation. This includes missing or misplaced semicolons, commas, or parentheses.
• Incorrect keywords or commands. This refers to using incorrect or misspelled language keywords.
• Improper use of language constructs. This involves using incorrect constructs or violating language-specific syntax rules.
• Wrong order of statements. This refers to having statements within a program that are arranged incorrectly or in a sequence that does not achieve the intended logic or functionality.

Example:

if x > 10
print("x is greater than 10"

Error: Missing “:” after the if statement.

  File "<string>", line 1
    if x > 10
            ^
 SyntaxError: invalid syntax

How to avoid syntax errors:

• Read error messages. Compilers and interpreters give error messages that show the location and type of syntax error. If you don't understand it, simply try to find an explanation in the resources, such as Stack Overflow.
• Use an integrated development environment (IDE) or plugins/extensions for code editors. Most modern IDEs highlight syntax errors in real-time, helping you identify and correct them early.
• Check language syntax rules. Refer to documentation or guides for the correct language syntax. 

2. Logic errors

Logic errors are a type of programming mistake in which the program runs but produces incorrect outcomes. Unlike syntax errors, logic errors do not usually cause a program to crash but instead lead to wrong or unexpected behavior. This makes them more challenging to locate and debug. Logic errors can be caused by various issues, such as:

• Incorrect conditionals. Using the wrong relational operators (e.g., using >= instead of >).
• Flawed loops. Creating infinite loops due to incorrect termination conditions.
• Miscalculations. Errors in mathematical calculations due to incorrect formulas or order of operations.
• Incorrect function calls or returns. Calling the wrong function or returning incorrect values.

Example:

x = 1

while (x < 10):
    print(x)

Error: Failed to update x before/after print(x), so an infinite loop appears.

Since this is a logical issue (not a syntax error), there won't be a specific error message produced by Python, but the loop will run indefinitely until manually stopped, typically with a keyboard interrupt (like pressing Ctrl+C).

How to avoid logic errors:

• Perform code reviews to catch logical errors that the original developer might miss. Peer review is the process of assessing work by one or more people who have similar expertise.
• Perform unit testing to validate that individual components of your code work as expected. Unit testing is the practice of evaluating the smallest independent piece of code - it will help to find modules, where logical errors occur.
• Accomplish step-by-step execution using debuggers to step through code line by line to observe the program's state and verify the logic. Debuggers are already integrated into most IDEs.
• Add assertions in the code to check expectations and constants during execution. Assertions will help you to check the values of variables at the moment. After inspecting, delete or comment out this part for clean code practice.

3. Memory leaks

Memory leaks happen when a program reserves memory for temporary use but doesn't release it back to the system when it's no longer needed. This can cause the program to use more and more memory over time, leading to a situation where available memory resources are depleted and the program or even the entire system slows down or crashes. They can be caused by a variety of issues such as:

• Failure to deallocate memory. This happens when dynamically allocated memory is not freed after use.
• Lost references. This occurs when the ability to free memory is lost due to pointers to allocated memory being overwritten or going out of scope.
• Circular references. This involves having objects that reference each other but are no longer reachable by the program, causing memory to remain allocated.
• Resource management errors. This includes incorrect handling of resources such as file handles, sockets, or other system resources that require explicit release.

Example:

f = open("example.txt", "r")
print(f.read())

Error: Forgetting to close the file (f.close()) leads to resource leakage.

How to avoid memory leaks:

• Make use of garbage collection. Use languages with garbage collection (e.g. Java) to handle memory management automatically.
• Use smart pointers. In C++ language, use smart pointers that automatically manage memory allocation and deallocation.
• Follow manual memory management discipline. In languages without automatic memory management (e.g. C++), strictly follow conventions for allocating and freeing memory (see example in Python above).
• Perform code reviews. Perform code reviews to identify potential leaks and use automated tests to confirm that memory is managed correctly.

4. Security vulnerabilities

Security vulnerabilities are weaknesses or defects that attackers can exploit to compromise the integrity, confidentiality, or availability of software, its data, or the systems it operates on.

These vulnerabilities can be caused due to a variety of issues, including:

• Buffer overflow. This occurs when a program writes more data to a buffer than it can hold, causing it to overwrite surrounding memory.
• SQL injection. This happens when attackers insert or manipulate SQL queries in input fields to execute arbitrary SQL code on the database.
• Cross-site scripting. This enables attackers to inject malicious scripts into web pages viewed by other users.
• Cross-site request forgery. This tricks authenticated users into executing unwanted actions on a web application by making them click on a malicious link or load a page.

Example:

user_input = input("Enter filename: ")
with open(user_input, 'r') as file:
    content = file.read()

Error: An attacker can enter a path like /etc/passwd to read sensitive system files. 

How to avoid security vulnerabilities:

• Input validation. Make sure to validate and sanitize user inputs to prevent malicious data from being processed. 
• Use security libraries. Utilize well-established security libraries and frameworks that offer built-in protection against common vulnerabilities. 
• Use strong authentication mechanisms. Implement robust authentication methods, such as multi-factor authentication, and ensure proper authorization checks. 
• Data encryption. Encrypt sensitive data both in transit and at rest.

5. Boundary condition errors

Boundary condition errors occur when values at the extreme ends (boundaries) of input ranges or data limits are mishandled or overlooked. These errors usually happen when developers forget to check or adequately test scenarios involving boundary values. Proper handling of boundary conditions is essential since they often involve edge cases that can result in unexpected behavior or vulnerabilities if not handled correctly. 

These errors can be caused by a variety of issues, such as:

• Off-by-one errors. These occur when iterating through an array or collection, and the loop stops or starts incorrectly due to incorrect boundary conditions.
• Indexing errors. These occur when accessing arrays, lists, or strings with indexes that exceed their bounds.
• Floating point precision. This refers to incorrectly handling floating-point comparisons near boundaries due to precision issues.
• Resource limits. This refers to ignoring or mishandling limits on resources such as memory, file handles, or network connections.

Example:

data = [10, 20, 30, 40, 50]
print(data[5])

Error: Index 5 is out of bounds (valid indexes are from 0 to 4).

Traceback (most recent call last):
  File "script.py", line 2, in <module>
    print(data[5])
IndexError: list index out of range

How to avoid boundary condition errors:

Write test cases that specifically target boundary conditions and edge cases and static and dynamic analysis tools to detect potential boundary issues. Boundary value analysis looks at:

• Minimum value
• Just below the minimum value
• Maximum value
• Just above the maximum value

The bottom line

To prevent software bugs, it is essential to implement an effective software QA strategy that combines good coding practices, various software testing types, and the use of modern tools and frameworks. By understanding common software bugs and implementing strategies to avoid them, you can significantly improve the quality and reliability of your software.

Investing time in code reviews, automated testing, and utilizing robust development environments will be beneficial in the long run, ensuring that your software is both functional and adaptable. It's important to remember that the goal is not just to find bugs but to prevent them.

Tired of dealing with software bugs that slow down your development process? Contact our team to discover how our comprehensive testing strategies ensure that your software is stable, efficient, and bug-free.