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!

Best regards,
Andrew