Debugging Applications with GDB

GDB, the GNU Debugger, is a powerful tool for debugging applications written in C, C++, and other programming languages. It allows you to inspect your program during runtime, providing insights into variables, memory, and control flow. This tutorial will guide you through the basics of using GDB for debugging your applications.

Prerequisites

• Basic knowledge of C or C++ programming.
• A Linux system with GDB installed.
• The application you want to debug.

1. Installing GDB

GDB is usually available in the default repositories. To install GDB, use the following commands based on your distribution:

• For Ubuntu/Debian:

  sudo apt update
  sudo apt install gdb -y

• For CentOS/RHEL:

  sudo yum install gdb -y

• For Fedora:

  sudo dnf install gdb -y

2. Compiling Your Application with Debugging Symbols

To use GDB effectively, you need to compile your application with debugging symbols. This is done by including the -g flag when compiling your code:

gcc -g -o myapp myapp.c

This will generate a binary named myapp with debugging information included.

3. Starting GDB

To start debugging your application, launch GDB with the executable:

gdb ./myapp

This command enters the GDB shell, where you can start issuing debugging commands.

4. Basic GDB Commands

Here are some essential commands to get started with GDB:

• run (r): Starts the execution of your program.

  run

• break (b): Sets a breakpoint at a specific line or function, pausing execution there.

  break main

• continue (c): Resumes execution until the next breakpoint.

  continue

• step (s): Executes the next line of code, stepping into functions.

  step

• next (n): Executes the next line of code, skipping over functions.

  next

• print (p): Displays the value of a variable or expression.

  print my_variable

• quit (q): Exits GDB.

  quit

5. Inspecting Variables and Memory

While debugging, you can inspect variables and memory addresses:

print variable_name          # Print variable value
x/y address                 # Examine memory at a specific address

To see a list of current variable values, you can also use:

info locals

6. Viewing the Call Stack

To view the current function call stack, use:

backtrace (bt)

This will show you the sequence of function calls that led to the current point of execution.

7. Modifying Program Execution

You can modify the value of variables as well during debugging:

set variable_name = new_value

This can be useful to test how your program reacts to different inputs while troubleshooting.

8. Conclusion

GDB is a powerful tool for debugging C and C++ applications, allowing you to step through code, inspect variables, and control execution flow. By following this tutorial, you are now equipped with the basic knowledge to use GDB effectively for debugging your applications. Continue exploring GDB’s features and integrate it into your development workflow for better debugging efficiency.

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Dorian Kane

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