Introduction

GDB is a powerful command line tool that can be used to debug programs written in C, C++, and other languages.

Despite its popularity, GDB can be quite intimidating for new users and especially for people just starting with C/C++. The existing guides and tutorials provide a lot of information, but they can be a bit too verbose for beginners. With this post I aim to provide a quick tutorial/reference for the most commonly used GDB commands for myself and others.

For the below commands, I also recommend to use shortcuts to optimize the workflow, e.g. use r instead of run, b instead of break, etc.

Commands

Quick list, sorted by usage

You probably don't have all day to read the entire post, so here is a quick list of commands sorted by usage:

• run or r - Start the program
• quit or q - Quit GDB
• break or b - Set a breakpoint
• continue or c - Continue execution
• next or n - Step over
• step or s - Step into
• Enter key - Repeat last command
• set or s - Change value of variable (super useful)
• print or p - Print value of variable
• backtrace or bt - Print backtrace
• list or l - List source code

Detailed list

Here's expanded list of commands with more details.

Starting the program

Note: r will start the program with the last used arguments, from the beginning. Useful if you want to restart the program with the same arguments.

• run or r - Start the program
• run <args> - Start the program with arguments
• run < <file> - Start the program with input from file

Quitting GDB

Note: You can also use Ctrl + D to quit GDB

• quit or q - Quit GDB

Breakpoints

• break <function> - Set a breakpoint at function
• break <file>:<function> - Set a breakpoint at function in specified file
• break <line> - Set a breakpoint at line number in current file
• break <file>:<line> - Set a breakpoint at line number in specified file
• break - List all breakpoints

Running the program

Note: continue will continue the program until the next breakpoint

• continue or c - Continue execution
• next or n - Step over
• step or s - Step into

Printing values

Note: sometimes it is easier to backtrace (bt) to see the values of variables at the current point

• print <variable> or p <variable> - Print value of variable
• print <expression> - Print value of expression
• print *<pointer> - Print value of pointer

Backtrace

• backtrace or bt - Print backtrace
• backtrace full or bt full - Print backtrace with arguments and local variables

Listing source code

• list or l - List source code
• list <function> - List source code of function
• list <file>:<line> - List source code around line number in specified file

Displaying source code

• display <variable> - Display value of variable after each step
• undisplay <display number> - Remove display

Changing values

• set <variable> = <value> - Change value of variable
• set $<register> = <value> - Change value of register

Conclusion

Hopefully this helped you get started or get a refresher on GDB. If you have any questions or suggestions, feel free to contact me.
Don't forget to drink water and take breaks while debugging!

Check the original article on my website arwo.xyz/gdb-guide

Best regards,
Andrew