GDB and CGDB Cheat Sheet

GDB (GNU Debugger)

GDB is a powerful tool for debugging applications written in C, C++, and other languages. Here’s a quick reference to some commonly used commands:

Basic Commands

• gdb [program] - Start GDB with the specified program.
• run [args] - Run the program with optional arguments.
• break [location] - Set a breakpoint at the specified location (function, line number, etc.).
• continue - Continue execution until the next breakpoint.
• next - Execute the next line of the program (step over).
• step - Step into a function.
• list - Show the source code around the current line.
• print [expression] - Evaluate and print the expression.
• info breakpoints - List all breakpoints.
• delete breakpoints [number] - Delete a specific breakpoint.
• quit - Exit GDB.

Advanced Commands

• watch [var] - Set a watchpoint for a variable.
• backtrace - Show the call stack.
• frame [number] - Select a frame from the call stack.
• set variable [var]=[value] - Set a variable to a new value.
• disassemble [function] - Show assembly code for the function.
• catch [event] - Break on specific events like throw or catch.
• info registers - Display the contents of CPU registers.
• info threads - List all threads.
• thread [number] - Switch to a specific thread.
• thread apply all [command] - Apply a command to all threads.
• set logging on - Enable logging of GDB session to a file.
• set follow-fork-mode [mode] - Control whether GDB follows the parent or child process after a fork.

Tips and Tricks

• Conditional Breakpoints: Set breakpoints that only trigger when a condition is met.

    break [location] if [condition]
  

• Command Lists: Execute a list of commands when a breakpoint is hit.

    break [location]
    commands
    [command1]
    [command2]
    end
  

• Pretty Printing: Enable pretty printing for complex data structures.

    set print pretty on
  

• Reverse Debugging: Step backwards in the program execution (requires GDB to be configured with reverse debugging support).

    target record
    reverse-step
    reverse-continue
  

CGDB (Curses-based interface to the GNU Debugger)

CGDB provides a more user-friendly interface to GDB. It includes split views showing source code and GDB commands simultaneously.

Key Bindings

• F7 - Step into a function (step in GDB).
• F8 - Step over a function (next in GDB).
• F9 - Set or clear a breakpoint at the current line.
• F10 - Continue program execution (continue in GDB).
• Ctrl + L - Redraw the screen.
• Tab - Switch between source and GDB command window.

Using CGDB

• Launching: cgdb [program]
• In the source window, you can navigate the code just like in a text editor.
• In the GDB command window, you can type any GDB command.

Tips for CGDB

• CGDB remembers the history of GDB commands; use the arrow keys to navigate through past commands.
• The split screen allows simultaneous viewing of source code and real-time debugging output, enhancing the debugging experience.

• Custom Key Bindings: Customize key bindings in CGDB by editing the .cgdb/cgdbrc file.

    bind key [key] [command]
  

• Macros: Define macros in CGDB to automate repetitive tasks.

    define [macro-name]
    [command1]
    [command2]
    end
  

• Color Schemes: Customize the color scheme of CGDB by editing the .cgdb/cgdb.conf file.

    set color [element] [color]
  

By leveraging these advanced commands and tips, you can significantly enhance your debugging efficiency and effectiveness with GDB and CGDB.