GDB(1)                       GNU Development Tools                      GDB(1)



NAME
       gdb - The GNU Debugger

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

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@t{++}, Fortran and
       Modula-2.

       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
               gdb -p 1234

       would attach GDB to process 1234 (unless you also have a file named
       1234; GDB does check for a core file first).  With option -p you can
       omit the program filename.

       Here are some of the most frequently needed GDB commands:

       break [file:]functiop
           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.

       -ex command
           Execute given GDB command.

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

       -nh Do not execute commands from ~/.gdbinit.

       -nx
       -n  Do not execute commands from any .gdbinit initialization files.

       -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 \032 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 \032 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
       The full documentation for GDB is maintained as a Texinfo manual.  If
       the "info" and "gdb" programs and GDB's Texinfo documentation are
       properly installed at your site, the command

               info gdb

       should give you access to the complete manual.

       Using GDB: A Guide to the GNU Source-Level Debugger, Richard M.
       Stallman and Roland H. Pesch, July 1991.

COPYRIGHT
       Copyright (c) 1988-2014 Free Software Foundation, Inc.

       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.3 or
       any later version published by the Free Software Foundation; with the
       Invariant Sections being "Free Software" and "Free Software Needs Free
       Documentation", with the Front-Cover Texts being "A GNU Manual," and
       with the Back-Cover Texts as in (a) below.

       (a) The FSF's Back-Cover Text is: "You are free to copy and modify this
       GNU Manual.  Buying copies from GNU Press supports the FSF in
       developing GNU and promoting software freedom."



gdb-7.7.1                         2014-05-05                            GDB(1)

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