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gdb(1)                             GNU Tools                            gdb(1)


       gdb - The GNU Debugger


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


       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:

          o   Start your program, specifying anything that  might  affect  its

          o   Make your program stop on specified conditions.

          o   Examine what has happened, when your program has stopped.

          o   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

       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

       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-

       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.


       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


       -h     List all options, with brief explanations.


       -s file
               Read symbol table from file file.

       -write Enable writing into executable and core files.


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

                Read  symbol table from file file and use it as the executable


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


       -x file
               Execute GDB commands from file file.


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


       -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.


       -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.

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


       -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.

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


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

       Further  documentation  is  available  in  /Applications/


       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  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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