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
              correcting the effects of one bug and go on to learn about

       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

       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

       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.


       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
              appropriate, and for examining pure data in conjunction with a
              core dump.

              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
              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.

              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
              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.

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


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


       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.

GNU Tools                          22may2002                            gdb(1)

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