🐞 C Debugging with GDB – A Developer’s Guide to Runtime Troubleshooting

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🧲 Introduction – Why GDB Matters in C Programming

When writing C programs, bugs such as segmentation faults, unexpected output, or memory corruption are inevitable. That’s where GDB (GNU Debugger) comes in. GDB is a powerful command-line debugging tool that helps developers inspect, monitor, and control the execution of C programs.

🎯 In this guide, you’ll learn:

• What GDB is and how it works
• How to set breakpoints and step through code
• How to inspect variables and memory
• Use cases for crash diagnosis and runtime analysis

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🧪 What Is GDB?

GDB stands for GNU Debugger, a tool used to debug C and C++ programs. It allows you to:

• Pause execution at specific points (breakpoints)
• Step through your code line by line
• View variable values and memory states
• Investigate segmentation faults or crashes
• Analyze core dumps

GDB is usually used with GCC-compiled programs and runs on Linux, Unix, and Windows (via MinGW or WSL).

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⚙️ GDB Core Commands & Features

Command	Purpose
gdb program_name	Start GDB with your compiled program
break <line> or b	Set a breakpoint at a specific line or function
run or r	Start program execution within GDB
next or n	Execute the next line (without entering functions)
step or s	Step into a function call
continue or c	Resume execution until the next breakpoint
print var or p var	Print the value of a variable
backtrace or bt	Show call stack trace
quit	Exit GDB

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💻 Example – Debugging a Segmentation Fault

#include <stdio.h>

int main() {
    int *ptr = NULL;
    *ptr = 5;  // Intentional segfault
    return 0;
}

🔍 Steps to Debug with GDB:

1. Compile with debug info: gcc -g program.c -o program
2. Start GDB: gdb ./program
3. Run the program inside GDB: (gdb) run
4. GDB will stop at the fault and display the location of the error: Program received signal SIGSEGV, Segmentation fault.
5. View stack trace: (gdb) backtrace
6. Inspect variable: (gdb) print ptr

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📚 Real-World Use Cases

Scenario	Why GDB Helps
Segmentation faults	Pinpoints exact crash line and call stack
Variable tracing	Shows real-time variable state at any point
Memory corruption	Helps detect invalid reads/writes
Loop diagnostics	Trace loop conditions and logic paths
Debugging core dumps	Inspect post-crash memory states (gdb prog core)

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💡 Best Practices & Tips

💡 Always compile with -g for debug symbols:

gcc -g mycode.c -o mycode

💡 Use break main or break <function> to stop at meaningful places early.

⚠️ Avoid using next blindly inside loops—use watch or condition for deeper control.

📘 Use GDB scripts to automate repetitive debugging steps.

💡 You can debug core dumps by running:

gdb ./myprogram core

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📌 Summary – Recap & Next Steps

GDB is an essential tool in every C programmer’s toolbox. It empowers you to identify, trace, and fix runtime errors with precision and control.

🔍 Key Takeaways:

• Use break, step, next, print, and backtrace to navigate runtime behavior.
• Compile with -g to include debug symbols.
• Analyze core dumps for post-crash investigations.
• Use GDB for real-time and post-mortem debugging.

⚙️ Real-World Relevance:

Widely used in embedded development, systems programming, Linux kernel modules, and performance tuning.

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❓ Frequently Asked Questions (FAQ)

❓ What is GDB used for?

✅ GDB is used to pause and analyze the state of a C program during execution to debug errors like segmentation faults, incorrect logic, or crashes.

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❓ How do I compile a C program for debugging?

✅ Use the -g flag with GCC:

gcc -g mycode.c -o mycode

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❓ What’s the difference between step and next?

✅ step enters into functions, while next executes the function without stepping into it.

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❓ Can I use GDB with code compiled in release mode?

✅ Technically yes, but without -g, symbol names and line numbers won’t be available—making debugging difficult.

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❓ How do I debug a core dump with GDB?

✅ Run:

gdb ./program core

Then use bt to see the stack trace.

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