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gdb(1)				   GNU Tools				gdb(1)

NAME
       gdb - The GNU Debugger

SYNOPSIS
       gdb    [-help] [-nx] [-q] [-batch] [-cd=dir] [-f] [-b bps] [-tty=dev]
	      [-s symfile] [-e prog] [-se prog] [-c core] [-x cmds] [-d dir]
	      [prog[core|procID]]

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 cor‐
	      recting the effects of one bug and go on to learn about another.

       You can use GDB to debug programs written  in  C,  C++,	and  Modula-2.
       Fortran support will be added when a GNU Fortran compiler is ready.

       GDB is invoked with the shell command gdb.  Once started, it reads com‐
       mands 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

       would attach GDB to process 1234 (unless you also  have	a  file	 named
       `1234'; GDB does check for a core file first).

       Here are some of the most frequently needed GDB commands:

       break [file:]function
	       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 break‐
	      point).

       next   Execute next program line (after stopping); step over any	 func‐
	      tion 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	 func‐
	      tion 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
       Debugger, by Richard M. Stallman and Roland H. Pesch.  The same text is
       available online as the gdb entry in the info program.

OPTIONS
       Any arguments other than options specify an executable  file  and  core
       file  (or  process ID); that is, the first argument encountered with no
       associated option flag is equivalent to a `-se' option, and the second,
       if  any,	 is  equivalent	 to  a `-c' option if it's the name of a file.
       Many options have both long and short forms; both are shown here.   The
       long  forms are also recognized if you truncate them, so long as enough
       of the option is present to be unambiguous.  (If you  prefer,  you  can
       flag  option  arguments	with `+' rather than `-', though we illustrate
       the more usual convention.)

       All the options and command line arguments you give  are	 processed  in
       sequential order.  The order makes a difference when the `-x' option is
       used.

       -help

       -h     List all options, with brief explanations.

       -symbols=file

       -s file
	       Read symbol table from file file.

       -write Enable writing into executable and core files.

       -exec=file

       -e file
	       Use file file as the executable file to execute when  appropri‐
	      ate,  and	 for  examining	 pure  data in conjunction with a core
	      dump.

       -se=file
	       Read symbol table from file file and use it as  the  executable
	      file.

       -core=file

       -c file
	       Use file file as a core dump to examine.

       -command=file

       -x file
	       Execute GDB commands from file file.

       -directory=directory

       -d directory
	       Add directory to the path to search for source files.

       -nx

       -n     Do  not  execute	commands  from	any  `.gdbinit' initialization
	      files.  Normally, the commands in these files are executed after
	      all the command options and arguments have been processed.

       -quiet

       -q     ``Quiet''.   Do  not  print  the introductory and copyright mes‐
	      sages.  These messages are also suppressed in batch mode.

       -batch Run in batch mode.  Exit with status 0 after processing all  the
	      command files specified with `-x' (and `.gdbinit', if not inhib‐
	      ited).  Exit with nonzero status if an error occurs in executing
	      the GDB commands in the command files.

	      Batch  mode may be useful for running GDB as a filter, for exam‐
	      ple to download and run a program on another computer; in	 order
	      to make this more useful, the message

	      Program exited normally.

	      (which is ordinarily issued whenever a program running under GDB
	      control terminates) is not issued when running in batch mode.

       -cd=directory
	       Run GDB using directory as its working  directory,  instead  of
	      the current directory.

       -fullname

       -f     Emacs  sets  this	 option	 when it runs GDB as a subprocess.  It
	      tells GDB to output the full file name  and  line	 number	 in  a
	      standard,	 recognizable  fashion each time a stack frame is dis‐
	      played (which includes each time the program stops).  This  rec‐
	      ognizable	 format	 looks	like two ` 32' characters, followed by
	      the file name, line number and character position	 separated  by
	      colons,  and a newline.  The Emacs-to-GDB interface program uses
	      the two ` 32' characters as a signal to display the source  code
	      for the frame.

       -b bps  Set the line speed (baud rate or bits per second) of any serial
	      interface used by GDB for remote debugging.

       -tty=device
	       Run using device for your program's standard input and output.

SEE ALSO
       `gdb' entry in info; Using GDB: A Guide to the GNU Source-Level	Debug‐
       ger, Richard M. Stallman and Roland H. Pesch, July 1991.

COPYING
       Copyright (c) 1991, 2010 Free Software Foundation, Inc.

       Permission  is  granted	to make and distribute verbatim copies of this
       manual provided the copyright notice and	 this  permission  notice  are
       preserved on all copies.

       Permission  is granted to copy and distribute modified versions of this
       manual under the conditions for verbatim	 copying,  provided  that  the
       entire  resulting derived work is distributed under the terms of a per‐
       mission notice identical to this one.

       Permission is granted to copy and distribute translations of this  man‐
       ual into another language, under the above conditions for modified ver‐
       sions, except that this permission notice may be included  in  transla‐
       tions approved by the Free Software Foundation instead of in the origi‐
       nal English.

GNU Tools			   22may2002				gdb(1)
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