Table of Contents
gdb Quick Reference
What is gdb
According to GNU , GDB, the GNU Project debugger, allows you to see what is going on “inside” another program while it executes - or what another program was doing at the moment it crashed.
Compiling For gdb
gdb needs information that is not ordinarily provided by the compiler. So, if you want to use gdb you need to include the -g switch when compiling. For example:
g++ -c -g Driver.cpp
Starting gdb
To start gdb, simply enter the gdb command in a terminal window. It has one paramter, the name of the executable. For example:
gdb Driver
Basic gdb Commands
The following commands are listed in alphabetical order:
| Command | Purpose |
|---|---|
| Enter | Re-execute the previous gdb command |
| break xx | Set a breakpoint at line xx in the current file |
| break functionname | Set a breakpoint at the start of functionname |
| break classname::functionname | Set a breakpoint at the start of a method |
| break filename:xx | Set a breakpoint at line xx in a specified file |
| continue | Resume running/executing the program |
| disable xx | Disable breakpoint number xx |
| enable xx | Enable breakpoint number xx |
| help | Display a list of gdb commands |
| help command | Get help on a specific command |
| info break | List all breakpoints |
| info source | Show the name of the current source file |
| info sources | List the name of all source files in use |
| list | List the next source lines |
| list xx | List source lines starting at line xx |
| list xx,yy | List sources lines from xx to yy |
| list filename:xx | List source lines in the specified file starting at line xx |
| next | Execute the current statement and then stop |
| print variable | Print the value of a variable |
| quit | Quit gdb |
| run | Run/execute the program starting from the beginning |
| set variable = value | Assign a new value to a variable |
| step | Execute the current statement (entering a function if possible) |
A Sample Session
A small sample session of gdb (with an executable named Driver) might look something like the following [where $ is the shell prompt and (gdb) is the gdb prompt]:
$ gdb Driver (gdb) break 1 (gdb) run (gdb) next (gdb) print i (gdb) next (gdb) print i (gdb) quit