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:

	  o   Start your program, specifying anything that might affect its behavior.

	  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 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 com-
       mand 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  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 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.

GNU Tools							     22may2002								    gdb(1)