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  correcting
       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 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  speci-
  fied:

  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 breakpoint).

  next Execute next program line (after stopping);  step  over	any  function
       calls in the line.

  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
  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.


  -exec=file

  -e file
	Use file file as the executable file to execute when appropriate, 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 com-
       mand options and arguments have been processed.



  -quiet

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


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

       Batch mode may be useful for running GDB as a filter, for  example  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	 con-
       trol 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  displayed  (which
       includes each time the program stops).  This recognizable 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  Debugger,
  Richard M. Stallman and Roland H. Pesch, July 1991.

COPYING
  Copyright (c) 1991 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  permission
  notice identical to this one.

  Permission is granted to copy and distribute translations  of	 this  manual
  into	another	 language,  under the above conditions for modified versions,
  except that this permission notice may be included in translations approved
  by the Free Software Foundation instead of in the original English.