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C Debugging

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🐞 C Debugging

Debugging is the process of identifying and fixing errors (bugs) in a C program. Errors can be logical, runtime, or compile-time. Debugging helps ensure the program behaves as expected.

🔍 Why Debugging Is Important?

  • Helps locate incorrect logic

  • Prevents program crashes

  • Improves memory and performance

  • Ensures maintainable and error-free code

🧰 Debugging Methods in C

✔ 1. Using Print Statements (printf)

This is the simplest debugging method. You print variable values at certain points to track behavior.

Example:

#include <stdio.h>

int main() {
int a = 10, b = 0;
printf(“Before division: a=%d, b=%d\n”, a, b);

int result = a / b; // problematic line
printf(“Result = %d\n”, result);

return 0;
}

💡 Print statements help you pinpoint where the program goes wrong.

✔ 2. Using a Debugger (gdb)

gdb (GNU Debugger) helps:

  • Run a program step-by-step

  • Inspect variables

  • Set breakpoints

  • Track memory access

Compile with Debugging Info:

gcc -g program.c -o program

Run with gdb:

gdb ./program

Useful gdb Commands:

Command Meaning
run Start program
break main Stop at start of function
next Execute next line
print variable Display variable value
backtrace Show function call path
quit Exit debugger

✔ 3. Using an IDE Debugger

Modern IDEs include debugging tools:

  • Code::Blocks

  • DevC++

  • VS Code (with extensions)

  • CLion

  • Eclipse CDT

You can:

  • Add breakpoints

  • Inspect memory

  • Step through execution visually

✔ 4. Using Assertions

Assertions help detect unexpected conditions during runtime.

#include <stdio.h>
#include <assert.h>int main() {
int age = -5;

assert(age >= 0); // program stops if condition fails

printf(“Age: %d\n”, age);
return 0;
}

🔴 If the condition is false, the program stops and displays error details.

✔ 5. Static Analysis Tools

These tools scan code and detect:

  • Memory leaks

  • Unused variables

  • Undefined behavior

Popular tools:

  • clang-tidy

  • cppcheck

  • splint

Example:

cppcheck program.c

✔ 6. Memory Debugging Tools

Useful for detecting:

  • Memory leaks

  • Invalid memory access

  • Double free errors

Tool: Valgrind

valgrind ./program

🧪 Debugging Example Program

#include <stdio.h>

int main() {
int numbers[5];

for (int i = 0; i <= 5; i++) { // BUG: <= should be <
numbers[i] = i * 10;
printf(“numbers[%d] = %d\n”, i, numbers[i]);
}

return 0;
}

🛠 Debugging Thought Process:

Line Issue Fix
i <= 5 Writing outside array bounds Change to i < 5

Corrected:

for (int i = 0; i < 5; i++)

🧩 Debugging Tips

✔ Test small code blocks before full program
✔ Use clear variable names
✔ Avoid deeply nested loops
✔ Use comments
✔ Keep backup versions

🏁 Summary

Debugging Method Best For
Print statements Simple bug tracking
GDB Complex code and step debugging
Assertions Input validation and logic checks
Memory tools Detect memory leaks or pointer errors
IDE Debuggers Visual debugging

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Sanjit Sinha — Web Developer | PHP • Laravel • CodeIgniter • MySQL • Bootstrap Founder, CodeCapsule — Student projects & practical coding guides. Email: info@codecapsule.in • Website: CodeCapsule.in

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