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 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 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 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 commands 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 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, 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.