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 cor-
 recting 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 com-
 mands 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 break-
 point).
 next Execute next program line (after stopping); step over any func-
 tion 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 func-
 tion 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 appropri-
 ate, 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 mes-
 sages. 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 exam-
 ple 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 dis-
 played (which includes each time the program stops). This rec-
 ognizable 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 Debug-
 ger, Richard M. Stallman and Roland H. Pesch, July 1991.
 Further documentation is available in /Applications/Xcode.app/Con-
 tents/Developer/Documentation/DocSets/com.apple.ADC_Refer-
 ence_Library.DeveloperTools.docset/Contents/Resources/Documents/docu-
 mentation/DeveloperTools/gdb

COPYING

 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 per-
 mission notice identical to this one.
 Permission is granted to copy and distribute translations of this man-
 ual into another language, under the above conditions for modified ver-
 sions, except that this permission notice may be included in transla-
 tions approved by the Free Software Foundation instead of in the origi-
 nal English.
GNU Tools 22may2002 gdb(1)