GDB The GNU Project Debugger

GDB cheat sheet and useful stuff

• You can hit enter to execute the previously executed command
• Auto complete and command history using arrow keys usually works fine
• Make sure to add -DDEBUG and -ggdb options when compiling your code
• Basic usage: (1) run gdb, (2) set breakpoints then (3) run program
  1. gdb <app_name_here>
  2. (gdb) break <file_name_here>:<line_number_here>
     • b <function_name>
  3. (gdb) run
     • r <app command-line arguments>

Create a .in command file

• Call commands file: gdb --command <gdb_commands_file_here.in>
• .in commands file example:

# You can add commends to the filelike this
file ./<bin_executable_app_here>
break main
directory ./.
set print pretty on
set print union on
set print array on
set print array-indexes on
set args -t 60

GDB Commands

All these commands ca be executed once gdb is already running

Running and stepping

1. run or r: Run the currently opened executable
2. step or s: Execute next code line entering function calls
3. next or n: Execute next code line skipping function calls
4. finish: Continue running until the function that is currently being executed returns
5. until <line_number>: Run until a line number in the current context
6. until <file_name>:<line_number>: Run until a line number in the given file
7. continue: Continue program execution
8. quit or q: quits/exits GDB

Breaks

1. break <file_name>:<line_number>: Set breakpoint in a certain line number of a certain file
   • Ex. break MyClass.cpp:50
2. info breakpoints : Shows status and info of current breaks/breakpoints.
3. enable/disable <break_number>: Enables or disables a breakpoint
4. delete <break_number>: Removes a breakpoint

Display, print and other

1. print <variable_name> or p: Prints variable contents, the variable can be of any type
   • Ex. print MyVariable
   • Ex. p/x MyVariable : print in hex
2. set var <variable_name>=<value>: Set variable to the given value.
   • Ex. set var MyVariable=0x10
3. backtrace or bt: Prints function backtrace/callstack
4. display <variable_name/expression>: Adds variable/expression to the items that are displayed every time execution stops
   • Ex. display i
5. info display: Shows list and status of display items
6. info locals: Shows list of local variables
7. delete display <display_num>: Removes variable/expression from the items that are displayed every time execution stops