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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 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 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 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 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 dif-
       ference 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 appropriate, and for examining pure data  in  con-
              junction 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 messages.  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 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 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  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 debug-
              ging.


       -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, 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 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.



GNU Tools                          22may2002                            gdb(1)