Debugging in C

Debugging in C is locating, analyzing, and correcting mistakes, bugs, or other problems in a C program. These mistakes can be caused by syntax, logic, or runtime behaviour. Debugging is an important component of software development since it ensures that a program works properly and achieves the intended results.

Debugging is a methodical technique that assists engineers in identifying and resolving problems in their code. These flaws vary from syntax and logical errors to execution problems and crashes. Effective troubleshooting can save time and effort during a software project's building and maintenance phases.

What exactly is a bug?

According to Ko and Meyers (2004), a bug is a difference between the design of software and its implementation. We anticipated something different than what is happening.

Examples:

Expected factorial(5) to be 120, but it produced 0.
Expected program to finish successfully, but aborted and reported a "segmentation fault".

Types of Bugs

There are various types of bugs, including:

Compile-time errors: These arises during the compiler's compilation process whenever the code breaches syntax rules. Missing semicolons, undefined variables, and typos are a few examples.
Runtime Errors: These errors occur when the program is running. Division by zero, null pointer dereference, and overflowing buffers are common.
Errors in Logic: Debugging logic flaws is the most difficult. They occur when the program's logic is wrong, resulting in inaccurate results or unexpected behaviour.
Concurrency Issues: Debugging concurrency-related difficulties such as race situations and deadlocks in multiple-threaded or multi-process programs is difficult.

Debugging Methods

There are several methods for debugging. Some main methods for debugging are as follows:

Print Statements: Inserting print statements into the code for displaying the values of variables, calls to function, and control flows is one of the easiest debugging approaches. It allows you to follow the program's execution.
Interactive Debuggers: Debugging programs are specialized tools that allow a more systematic and collaborative approach to troubleshooting. GDB (GNU Debugger) is a popular C debugging tool. You can use it to set breakpoints, analyze variables, and walk through code.
Static Testing Tools: Tools like lint or static analyzers may identify possible mistakes without running the code. They can detect a wide range of common code errors.
Dynamic Analysis Tools: Dynamic analysis tools, such as storage profilers and sanitisers (e.g., AddressSanitizer), enable the detection of memory leaks, overflows of buffers, and other execution issues.

Debugging is usually done systematically:

Reproduce the Issue: Begin by comprehending the issue. Continuously reproduce the issue to comprehend the issue's scale and impact.
Identify the Issue: Determine the exact section of code where the problem occurs. Examining error message logs or utilizing a debugger is frequently required.
Determine the Root Cause: Determine the root cause when you've isolated the problem. It could be a logical error, bad data, or an improper function call.
Resolve the Problem: Create a solution to the bug. Check that the solution solves the root problem and does not bring new problems.
Test the correction: Once the correction has been implemented, extensively test the code to ensure the issue has been handled. It could include executing unit, integration, or user tests.
Regression Testing: Exercise caution while introducing new bugs and addressing existing ones. Regression testing should be performed to guarantee that existing functionality is not lost.
Documentation: Write out the bug, how it was fixed, and any lessons learned. This helps in the exchange of information and the prevention of similar problems in the future.

Tips and Best Practices for Debugging

There are several tips and best practices for debugging. Some main tips and best practices for debugging are as follows:

Use Version Control: Versioning systems such as Git help monitor changes, making it easier to determine when an issue was introduced.
Divide and Conquer: When facing complex issues, break the issue into numerous smaller elements.
Read Documentation: To obtain a greater understanding of libraries and APIs, read documentation, instructional materials, and error messages.
Code Reviews: Peer evaluations of code can detect bugs early and provide helpful ideas.
Remain Calm: Debugging can be exhausting. Stay cautious, take breaks, and avoid making quick changes that may bring new problems.
Test Environment: Ensuring your test and development platforms are as near to the production environments as possible.

Tools for Debugging

There are several tools for debugging. Some main tools for debugging are as follows:

GDB (GNU Debugger): GDB is a strong C and C++ command-line debugger. You can use it to set breakpoints, click inspect variables, and regulate program execution.
Valgrind: Valgrind is a toolset containing memory evaluation instruments, such as Memcheck, that can aid in detecting memory-related issues.
AddressSanitizer: During the runtime, this tool assists in identifying memory-related issues such as overflows of buffers and use-after-free errors.
Integrated Development Environments (IDEs): IDEs such as Visual Studio, CLion, and Code::Troubleshooting capabilities are built into blocks, which include graphical interfaces.
Static Analyzers: Tools such as cppcheck and Clang Static Analyzer can detect potential bugs in programs without running them.

Debugging is a crucial skill for a programmer, while working through real-world situations may be quite beneficial. Here are a few C programming examples with frequent troubleshooting circumstances and explanations:

1. Null Pointer Dereference:

Let's take a program for illustrating the null pointer dereference in C.

#include <stdio.h>
int main() {
 int* pt = NULL;
 *pt = 100; // Dereferencing a null pointer, causing a segmentation fault

 printf("This won't be reached.\n");
 return 0;
}

Output:

Segmentation fault (core dumped)

Issue: The program attempts to write to a memory area pointed to by an empty pointer, resulting in a segmentation error.

Debugging: Running this code via a debugger like GDB will pinpoint the exact line wherever a segmentation fault happens. Backtrace (or bt) can be used to observe the call stack, and print (or p) can be used to analyze variables.

2. Array index out of Bounds

Let's take a program for illustrating the array index out of bounds in C.

#include <stdio.h>
int main() {
 int array[5] = {10, 20, 30, 40, 50};
 printf("%d\n", array[10]); // Accessing an out-of-bounds array index

 return 0;
}

Output:

1989877136

Issues: The code is trying to access an array component that does not exist (out-of-bounds).

Debugging: Debugging tools will assist in determining the exact line of the problem. Use print (or p) to determine the value of arr and why the index is out of bounds.

3. Infinite loop

Let's take a program for illustrating the infinite loops in C.

#include <stdio.h>
int main() {
 int ind= 0;
 while (ind >= 0) {
 printf("Iteration %d\n", ind);
 ind++; // Forgetting to increment the loop control variable
 }

 return 0;
}

Output:

Iteration 51359
Iteration 51360
Iteration 51361
Iteration 51362
Iteration 51363
Iteration 51364
Iteration 51365
Iteration 51366
Iteration 51367
Iteration 51368
Iteration 51369
Iteration 51370
Iteration 51371
Iteration 51372
Iteration...

Issue: The loop becomes infinite because the loop control variable i nd is always larger than or equal to zero.

Debugging: Set breakpoints and examine the value of ind with a debugger. You'll note that i nd never decreases, which results in an unending loop.

4. Logic Error

Let's take a program to illustrate the logic error in C.

#include <stdio.h>
int main() {
 int m = 5;
 int n = 10;
 if (m > n) {
 printf("m is greater than n.\n");
 } else {
 printf("m is not greater than n.\n");
 }
 return 0;
}

Output:

m is not greater than n.

Issue: The code falsely claims that "m is not greater than n" when it is.

Debugging: There is no runtime issue in this situation. Debugging involves examining the logic and comparing it to expected behaviour to identify and rectify errors.

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