GDB(1) GNU Development Tools GDB(1)
NAME
gdb - The GNU Debugger
SYNOPSIS
gdb [-help] [-nh] [-nx] [-q] [-batch] [-cd=dir] [-f] [-b bps]
[-tty=dev] [-s symfile] [-e prog] [-se prog] [-c core] [-p procID]
[-x cmds] [-d dir] [prog|prog procID|prog core]
DESCRIPTION
The purpose of a debugger such as GDB is to allow you to see what is going on “inside” another program while it executes – or what another program was doing at the moment it crashed.
GDB can do four main kinds of things (plus other things in support of
these) to help you catch bugs in the act:
· Start your program, specifying anything that might affect its
behavior.
· Make your program stop on specified conditions.
· Examine what has happened, when your program has stopped.
· Change things in your program, so you can experiment with
correcting the effects of one bug and go on to learn about another.
You can use GDB to debug programs written in C, C@t{++}, Fortran and
Modula-2.
GDB is invoked with the shell command "gdb". Once started, it reads
commands from the terminal until you tell it to exit with the GDB
command "quit". You can get online help from GDB itself by using the
command "help".
You can run "gdb" with no arguments or options; but the most usual way
to start GDB is with one argument or two, specifying an executable
program as the argument:
gdb program
You can also start with both an executable program and a core file
specified:
gdb program core
You can, instead, specify a process ID as a second argument, if you
want to debug a running process:
gdb program 1234
gdb -p 1234
would attach GDB to process 1234 (unless you also have a file named
1234; GDB does check for a core file first). With option -p you can
omit the program filename.
Here are some of the most frequently needed GDB commands:
break [file:]functiop
Set a breakpoint at function (in file).
run [arglist]
Start your program (with arglist, if specified).
bt Backtrace: display the program stack.
print expr
Display the value of an expression.
c Continue running your program (after stopping, e.g. at a breakpoint).
next
Execute next program line (after stopping); step over any function
calls in the line.
edit [file:]function
look at the program line where it is presently stopped.
list [file:]function
type the text of the program in the vicinity of where it is
presently stopped.
step
Execute next program line (after stopping); step into any function
calls in the line.
help [name]
Show information about GDB command name, or general information
about using GDB.
quit
Exit from GDB.
For full details on GDB, see Using GDB: A Guide to the GNU Source-Level
available online as the "gdb" entry in the "info" program.