1 @c This is part of the Emacs manual.
2 @c Copyright (C) 1985,86,87,93,94,95,97,2000,2001 Free Software Foundation, Inc.
3 @c See file emacs.texi for copying conditions.
4 @node Building, Maintaining, Programs, Top
5 @chapter Compiling and Testing Programs
6 @cindex building programs
7 @cindex program building
8 @cindex running Lisp functions
10 The previous chapter discusses the Emacs commands that are useful for
11 making changes in programs. This chapter deals with commands that assist
12 in the larger process of developing and maintaining programs.
15 * Compilation:: Compiling programs in languages other
16 than Lisp (C, Pascal, etc.).
17 * Compilation Mode:: The mode for visiting compiler errors.
18 * Compilation Shell:: Customizing your shell properly
19 for use in the compilation buffer.
20 * Grep Searching:: Searching with grep.
21 * Flymake:: Finding syntax errors on the fly.
22 * Debuggers:: Running symbolic debuggers for non-Lisp programs.
23 * Executing Lisp:: Various modes for editing Lisp programs,
24 with different facilities for running
26 * Libraries: Lisp Libraries. Creating Lisp programs to run in Emacs.
27 * Eval: Lisp Eval. Executing a single Lisp expression in Emacs.
28 * Interaction: Lisp Interaction. Executing Lisp in an Emacs buffer.
29 * External Lisp:: Communicating through Emacs with a separate Lisp.
33 @section Running Compilations under Emacs
34 @cindex inferior process
36 @cindex compilation errors
39 Emacs can run compilers for noninteractive languages such as C and
40 Fortran as inferior processes, feeding the error log into an Emacs buffer.
41 It can also parse the error messages and show you the source lines where
42 compilation errors occurred.
46 Run a compiler asynchronously under Emacs, with error messages going to
47 the @samp{*compilation*} buffer.
49 Invoke a compiler with the same command as in the last invocation of
52 Run @code{grep} asynchronously under Emacs, with matching lines
53 listed in the buffer named @samp{*grep*}.
56 Run @code{grep} via @code{find}, with user-specified arguments, and
57 collect output in the buffer named @samp{*grep*}.
58 @item M-x kill-compilation
60 Kill the running compilation or @code{grep} subprocess.
64 To run @code{make} or another compilation command, do @kbd{M-x
65 compile}. This command reads a shell command line using the minibuffer,
66 and then executes the command in an inferior shell, putting output in
67 the buffer named @samp{*compilation*}. The current buffer's default
68 directory is used as the working directory for the execution of the
69 command; normally, therefore, the compilation happens in this
72 @vindex compile-command
73 When the shell command line is read, the minibuffer appears
74 containing a default command line, which is the command you used the
75 last time you did @kbd{M-x compile}. If you type just @key{RET}, the
76 same command line is used again. For the first @kbd{M-x compile}, the
77 default is @samp{make -k}, which is correct most of the time for
78 nontrivial programs. (@xref{Top,, Make, make, GNU Make Manual}.)
79 The default compilation command comes from the variable
80 @code{compile-command}; if the appropriate compilation command for a
81 file is something other than @samp{make -k}, it can be useful for the
82 file to specify a local value for @code{compile-command} (@pxref{File
85 Starting a compilation displays the buffer @samp{*compilation*} in
86 another window but does not select it. The buffer's mode line tells
87 you whether compilation is finished, with the word @samp{run},
88 @samp{signal} or @samp{exit} inside the parentheses. You do not have
89 to keep this buffer visible; compilation continues in any case. While
90 a compilation is going on, the string @samp{Compiling} appears in the
91 mode lines of all windows. When this string disappears, the
92 compilation is finished.
94 If you want to watch the compilation transcript as it appears, switch
95 to the @samp{*compilation*} buffer and move point to the end of the
96 buffer. When point is at the end, new compilation output is inserted
97 above point, which remains at the end. If point is not at the end of
98 the buffer, it remains fixed while more compilation output is added at
99 the end of the buffer.
101 @cindex compilation buffer, keeping current position at the end
102 @vindex compilation-scroll-output
103 If you set the variable @code{compilation-scroll-output} to a
104 non-@code{nil} value, then the compilation buffer always scrolls to
105 follow output as it comes in.
107 @findex kill-compilation
108 When the compiler process terminates, for whatever reason, the mode
109 line of the @samp{*compilation*} buffer changes to say @samp{exit}
110 (followed by the exit code, @samp{[0]} for a normal exit), or
111 @samp{signal} (if a signal terminated the process), instead of
112 @samp{run}. Starting a new compilation also kills any running
113 compilation, as only one can exist at any time. However, @kbd{M-x
114 compile} asks for confirmation before actually killing a compilation
115 that is running. You can also kill the compilation process with
116 @kbd{M-x kill-compilation}.
119 To rerun the last compilation with the same command, type @kbd{M-x
120 recompile}. This automatically reuses the compilation command from the
121 last invocation of @kbd{M-x compile}.
123 Emacs does not expect a compiler process to launch asynchronous
124 subprocesses; if it does, and they keep running after the main
125 compiler process has terminated, Emacs may kill them or their output
126 may not arrive in Emacs. To avoid this problem, make the main process
127 wait for its subprocesses to finish. In a shell script, you can do this
128 using @samp{$!} and @samp{wait}, like this:
131 (sleep 10; echo 2nd)& pid=$! # @r{Record pid of subprocess}
133 wait $pid # @r{Wait for subprocess}
136 If the background process does not output to the compilation buffer,
137 so you only need to prevent it from being killed when the main
138 compilation process terminates, this is sufficient:
141 nohup @var{command}; sleep 1
144 @vindex compilation-environment
145 You can control the environment passed to the compilation command
146 with the variable @code{compilation-environment}. Its value is a list
147 of environment variable settings; each element should be a string of
148 the form @code{"@var{envvarname}=@var{value}"}. These environment
149 variable settings override the usual ones.
151 @node Compilation Mode
152 @section Compilation Mode
154 @findex compile-goto-error
155 @cindex Compilation mode
156 @cindex mode, Compilation
157 The @samp{*compilation*} buffer uses a special major mode, Compilation
158 mode, whose main feature is to provide a convenient way to look at the
159 source line where the error happened.
161 If you set the variable @code{compilation-scroll-output} to a
162 non-@code{nil} value, then the compilation buffer always scrolls to
163 follow output as it comes in.
167 Visit the locus of the next compiler error message or @code{grep} match.
169 Visit the locus of the error message that point is on.
170 This command is used in the compilation buffer.
172 Visit the locus of the error message that you click on.
174 Find and highlight the locus of the next error message, without
175 selecting the source buffer.
177 Find and highlight the locus of the previous error message, without
178 selecting the source buffer.
180 Move point to the next error for a different file than the current
183 Move point to the previous error for a different file than the current
186 Toggle Next Error Follow minor mode, which makes cursor motion in the
187 compilation buffer produce automatic source display.
192 You can visit the source for any particular error message by moving
193 point in the @samp{*compilation*} buffer to that error message and
194 typing @key{RET} (@code{compile-goto-error}). Alternatively, you can
195 click @kbd{Mouse-2} on the error message; you need not switch to the
196 @samp{*compilation*} buffer first.
198 @vindex next-error-highlight
199 To parse the compiler error messages sequentially, type @kbd{C-x `}
200 (@code{next-error}). The character following the @kbd{C-x} is the
201 backquote or ``grave accent,'' not the single-quote. This command is
202 available in all buffers, not just in @samp{*compilation*}; it
203 displays the next error message at the top of one window and source
204 location of the error in another window. It also momentarily
205 highlights the relevant source line. You can change the behavior of
206 this highlighting with the variable @code{next-error-highlight}.
208 The first time @kbd{C-x `} is used after the start of a compilation,
209 it moves to the first error's location. Subsequent uses of @kbd{C-x `}
210 advance down to subsequent errors. If you visit a specific error
211 message with @key{RET} or @kbd{Mouse-2}, subsequent @kbd{C-x `}
212 commands advance from there. When @kbd{C-x `} gets to the end of the
213 buffer and finds no more error messages to visit, it fails and signals
216 You don't have to be in the compilation buffer in order to use
217 @code{next-error}. If one window on the selected frame can be the
218 target of the @code{next-error} call, it is used. Else, if a buffer
219 previously had @code{next-error} called on it, it is used. Else,
220 if the current buffer can be the target of @code{next-error}, it is
221 used. Else, all the buffers Emacs manages are tried for
222 @code{next-error} support.
224 @kbd{C-u C-x `} starts scanning from the beginning of the compilation
225 buffer. This is one way to process the same set of errors again.
227 @vindex compilation-error-regexp-alist
228 @vindex grep-regexp-alist
229 To parse messages from the compiler, Compilation mode uses the
230 variable @code{compilation-error-regexp-alist} which lists various
231 formats of error messages and tells Emacs how to extract the source file
232 and the line number from the text of a message. If your compiler isn't
233 supported, you can tailor Compilation mode to it by adding elements to
234 that list. A similar variable @code{grep-regexp-alist} tells Emacs how
235 to parse output of a @code{grep} command.
237 @findex compilation-next-error
238 @findex compilation-previous-error
239 @findex compilation-next-file
240 @findex compilation-previous-file
241 Compilation mode also redefines the keys @key{SPC} and @key{DEL} to
242 scroll by screenfuls, and @kbd{M-n} (@code{compilation-next-error})
243 and @kbd{M-p} (@code{compilation-previous-error}) to move to the next
244 or previous error message. You can also use @kbd{M-@{}
245 (@code{compilation-next-file} and @kbd{M-@}}
246 (@code{compilation-previous-file}) to move up or down to an error
247 message for a different source file.
249 @cindex Next Error Follow mode
250 @findex next-error-follow-minor-mode
251 You can type @kbd{C-c C-f} to toggle Next Error Follow mode. In
252 this minor mode, ordinary cursor motion in the compilation buffer
253 automatically updates the source buffer. For instance, moving the
254 cursor to the next error message causes the location of that error to
255 be displayed immediately.
257 The features of Compilation mode are also available in a minor mode
258 called Compilation Minor mode. This lets you parse error messages in
259 any buffer, not just a normal compilation output buffer. Type @kbd{M-x
260 compilation-minor-mode} to enable the minor mode. This defines the keys
261 @key{RET} and @kbd{Mouse-2}, as in the Compilation major mode.
263 Compilation minor mode works in any buffer, as long as the contents
264 are in a format that it understands. In an Rlogin buffer (@pxref{Remote
265 Host}), Compilation minor mode automatically accesses remote source
266 files by FTP (@pxref{File Names}).
268 @node Compilation Shell
269 @section Subshells for Compilation
271 Emacs uses a shell to run the compilation command, but specifies
272 the option for a noninteractive shell. This means, in particular, that
273 the shell should start with no prompt. If you find your usual shell
274 prompt making an unsightly appearance in the @samp{*compilation*}
275 buffer, it means you have made a mistake in your shell's init file by
276 setting the prompt unconditionally. (This init file's name may be
277 @file{.bashrc}, @file{.profile}, @file{.cshrc}, @file{.shrc}, or various
278 other things, depending on the shell you use.) The shell init file
279 should set the prompt only if there already is a prompt. In csh, here
283 if ($?prompt) set prompt = @dots{}
287 And here's how to do it in bash:
290 if [ "$@{PS1+set@}" = set ]
295 There may well be other things that your shell's init file
296 ought to do only for an interactive shell. You can use the same
297 method to conditionalize them.
299 The MS-DOS ``operating system'' does not support asynchronous
300 subprocesses; to work around this lack, @kbd{M-x compile} runs the
301 compilation command synchronously on MS-DOS. As a consequence, you must
302 wait until the command finishes before you can do anything else in
303 Emacs. @xref{MS-DOS}.
306 @section Searching with Grep under Emacs
309 Just as you can run a compiler from Emacs and then visit the lines
310 where there were compilation errors, you can also run @code{grep} and
311 then visit the lines on which matches were found. This works by
312 treating the matches reported by @code{grep} as if they were ``errors.''
314 To do this, type @kbd{M-x grep}, then enter a command line that
315 specifies how to run @code{grep}. Use the same arguments you would give
316 @code{grep} when running it normally: a @code{grep}-style regexp
317 (usually in single-quotes to quote the shell's special characters)
318 followed by file names, which may use wildcards. If you specify a
319 prefix argument for @kbd{M-x grep}, it figures out the tag
320 (@pxref{Tags}) around point, and puts that into the default
323 The output from @code{grep} goes in the @samp{*grep*} buffer. You
324 can find the corresponding lines in the original files using @kbd{C-x
325 `}, @key{RET}, and so forth, just like compilation errors.
327 Some grep programs accept a @samp{--color} option to output special
328 markers around matches for the purpose of highlighting. You can make
329 use of this feature by setting @code{grep-highlight-matches} to t.
330 When displaying a match in the source buffer, the exact match will be
331 highlighted, instead of the entire source line.
335 The command @kbd{M-x grep-find} (also available as @kbd{M-x
336 find-grep}) is similar to @kbd{M-x grep}, but it supplies a different
337 initial default for the command---one that runs both @code{find} and
338 @code{grep}, so as to search every file in a directory tree. See also
339 the @code{find-grep-dired} command, in @ref{Dired and Find}.
342 @section Finding Syntax Errors On The Fly
343 @cindex checking syntax
345 Flymake mode is a minor mode that performs on-the-fly syntax
346 checking for many programming and markup languages, including C, C++,
347 Perl, HTML, and @TeX{}/La@TeX{}. It is somewhat analogous to Flyspell
348 mode, which performs spell checking for ordinary human languages in a
349 similar fashion (@pxref{Spelling}). As you edit a file, Flymake mode
350 runs an appropriate syntax checking tool in the background, using a
351 temporary copy of the buffer. It then parses the error and warning
352 messages, and highlights the erroneous lines in the buffer. The
353 syntax checking tool used depends on the language; for example, for
354 C/C++ files this is usually the C compiler. Flymake can also use
355 build tools such as @code{make} for checking complicated projects.
357 To activate Flymake mode, type @kbd{M-x flymake-mode}. You can move
358 to the errors spotted by Flymake mode with @kbd{M-x
359 flymake-goto-next-error} and @kbd{M-x flymake-goto-prev-error}. To
360 display any error messages associated with the current line, use
361 @kbd{M-x flymake-display-err-menu-for-current-line}.
363 For more details about using Flymake, see @ref{Top, Flymake,
364 Flymake, flymake, The Flymake Manual}.
367 @section Running Debuggers Under Emacs
379 @c Do you believe in GUD?
380 The GUD (Grand Unified Debugger) library provides an interface to
381 various symbolic debuggers from within Emacs. We recommend the
382 debugger GDB, which is free software, but you can also run DBX, SDB or
383 XDB if you have them. GUD can also serve as an interface to Perl's
384 debugging mode, the Python debugger PDB, the bash debugger, and to
385 JDB, the Java Debugger. @xref{Debugging,, The Lisp Debugger, elisp,
386 the Emacs Lisp Reference Manual}, for information on debugging Emacs
390 * Starting GUD:: How to start a debugger subprocess.
391 * Debugger Operation:: Connection between the debugger and source buffers.
392 * Commands of GUD:: Key bindings for common commands.
393 * GUD Customization:: Defining your own commands for GUD.
394 * GDB Graphical Interface:: An enhanced mode that uses GDB features to
395 implement a graphical debugging environment through
400 @subsection Starting GUD
402 There are several commands for starting a debugger, each corresponding
403 to a particular debugger program.
406 @item M-x gdb @key{RET} @var{file} @key{RET}
408 Run GDB as a subprocess of Emacs. By default, this operates in
409 graphical mode; @xref{GDB Graphical Interface}. Graphical mode
410 does not support any other debuggers.
412 @item M-x dbx @key{RET} @var{file} @key{RET}
414 Similar, but run DBX instead of GDB.
416 @item M-x xdb @key{RET} @var{file} @key{RET}
418 @vindex gud-xdb-directories
419 Similar, but run XDB instead of GDB. Use the variable
420 @code{gud-xdb-directories} to specify directories to search for source
423 @item M-x sdb @key{RET} @var{file} @key{RET}
425 Similar, but run SDB instead of GDB.
427 Some versions of SDB do not mention source file names in their
428 messages. When you use them, you need to have a valid tags table
429 (@pxref{Tags}) in order for GUD to find functions in the source code.
430 If you have not visited a tags table or the tags table doesn't list one
431 of the functions, you get a message saying @samp{The sdb support
432 requires a valid tags table to work}. If this happens, generate a valid
433 tags table in the working directory and try again.
435 @item M-x bashdb @key{RET} @var{file} @key{RET}
437 Run the bash debugger to debug @var{file}, a shell script.
439 @item M-x perldb @key{RET} @var{file} @key{RET}
441 Run the Perl interpreter in debug mode to debug @var{file}, a Perl program.
443 @item M-x jdb @key{RET} @var{file} @key{RET}
445 Run the Java debugger to debug @var{file}.
447 @item M-x pdb @key{RET} @var{file} @key{RET}
449 Run the Python debugger to debug @var{file}.
452 Each of these commands takes one argument: a command line to invoke
453 the debugger. In the simplest case, specify just the name of the
454 executable file you want to debug. You may also use options that the
455 debugger supports. However, shell wildcards and variables are not
456 allowed. GUD assumes that the first argument not starting with a
457 @samp{-} is the executable file name.
459 @node Debugger Operation
460 @subsection Debugger Operation
462 @cindex fringes, and current execution line in GUD
463 When you run a debugger with GUD, the debugger uses an Emacs buffer
464 for its ordinary input and output. This is called the GUD buffer. The
465 debugger displays the source files of the program by visiting them in
466 Emacs buffers. An arrow (@samp{=>}) in one of these buffers indicates
467 the current execution line.@footnote{Under a window system, the arrow
468 appears in the left fringe of the Emacs window.} Moving point in this
469 buffer does not move the arrow.
471 You can start editing these source files at any time in the buffers
472 that display them. The arrow is not part of the file's
473 text; it appears only on the screen. If you do modify a source file,
474 keep in mind that inserting or deleting lines will throw off the arrow's
475 positioning; GUD has no way of figuring out which line corresponded
476 before your changes to the line number in a debugger message. Also,
477 you'll typically have to recompile and restart the program for your
478 changes to be reflected in the debugger's tables.
480 If you wish, you can control your debugger process entirely through the
481 debugger buffer, which uses a variant of Shell mode. All the usual
482 commands for your debugger are available, and you can use the Shell mode
483 history commands to repeat them. @xref{Shell Mode}.
485 @cindex tooltips with GUD
486 @vindex tooltip-gud-modes
487 @vindex tooltip-gud-tips-p
488 The Tooltip facility (@pxref{Tooltips}) provides support for GUD@.
489 You activate this feature by setting the variable
490 @code{tooltip-gud-tips-p} to @code{t}. Then you can display a
491 variable's value in a tooltip simply by pointing at it with the mouse.
492 This operates in the GUD buffer and in source buffers with major modes
493 in the list @code{tooltip-gud-modes}.
495 @node Commands of GUD
496 @subsection Commands of GUD
498 The GUD interaction buffer uses a variant of Shell mode, so the
499 commands of Shell mode are available (@pxref{Shell Mode}). GUD mode
500 also provides commands for setting and clearing breakpoints, for
501 selecting stack frames, and for stepping through the program. These
502 commands are available both in the GUD buffer and globally, but with
503 different key bindings. It also has its own toolbar from which you
504 can invoke the more common commands by clicking on the appropriate
505 icon. This is particularly useful for repetitive commands like
506 gud-next and gud-step and allows the user to hide the GUD buffer.
508 The breakpoint commands are normally used in source file buffers,
509 because that is the easiest way to specify where to set or clear the
510 breakpoint. Here's the global command to set a breakpoint:
515 Set a breakpoint on the source line that point is on.
518 @kindex C-x C-a @r{(GUD)}
519 Here are the other special commands provided by GUD. The keys
520 starting with @kbd{C-c} are available only in the GUD interaction
521 buffer. The key bindings that start with @kbd{C-x C-a} are available in
522 the GUD interaction buffer and also in source files.
526 @kindex C-c C-l @r{(GUD)}
529 Display in another window the last line referred to in the GUD
530 buffer (that is, the line indicated in the last location message).
531 This runs the command @code{gud-refresh}.
534 @kindex C-c C-s @r{(GUD)}
537 Execute a single line of code (@code{gud-step}). If the line contains
538 a function call, execution stops after entering the called function.
541 @kindex C-c C-n @r{(GUD)}
544 Execute a single line of code, stepping across entire function calls
545 at full speed (@code{gud-next}).
548 @kindex C-c C-i @r{(GUD)}
551 Execute a single machine instruction (@code{gud-stepi}).
555 @kindex C-c C-r @r{(GUD)}
558 Continue execution without specifying any stopping point. The program
559 will run until it hits a breakpoint, terminates, or gets a signal that
560 the debugger is checking for (@code{gud-cont}).
564 @kindex C-c C-d @r{(GUD)}
567 Delete the breakpoint(s) on the current source line, if any
568 (@code{gud-remove}). If you use this command in the GUD interaction
569 buffer, it applies to the line where the program last stopped.
572 @kindex C-c C-t @r{(GUD)}
575 Set a temporary breakpoint on the current source line, if any.
576 If you use this command in the GUD interaction buffer,
577 it applies to the line where the program last stopped.
580 The above commands are common to all supported debuggers. If you are
581 using GDB or (some versions of) DBX, these additional commands are available:
585 @kindex C-c < @r{(GUD)}
588 Select the next enclosing stack frame (@code{gud-up}). This is
589 equivalent to the @samp{up} command.
592 @kindex C-c > @r{(GUD)}
595 Select the next inner stack frame (@code{gud-down}). This is
596 equivalent to the @samp{down} command.
599 If you are using GDB, these additional key bindings are available:
603 @kindex C-c C-r @r{(GUD)}
606 Start execution of the program (@code{gud-run}).
609 @kindex C-c C-u @r{(GUD)}
612 Continue execution to the current line. The program will run until
613 it hits a breakpoint, terminates, gets a signal that the debugger is
614 checking for, or reaches the line on which the cursor currently sits
618 @kindex TAB @r{(GUD)}
619 @findex gud-gdb-complete-command
620 With GDB, complete a symbol name (@code{gud-gdb-complete-command}).
621 This key is available only in the GUD interaction buffer, and requires
622 GDB versions 4.13 and later.
625 @kindex C-c C-f @r{(GUD)}
628 Run the program until the selected stack frame returns (or until it
629 stops for some other reason).
632 @kindex C-x C-a C-j @r{(GUD)}
634 Only useful in a source buffer, (@code{gud-jump}) transfers the
635 program's execution point to the current line. In other words, the
636 next line that the program executes will be the one where you gave the
637 command. If the new execution line is in a different function from
638 the previously one, GDB prompts for confirmation since the results may
639 be bizarre. See the GDB manual entry regarding @code{jump} for
643 These commands interpret a numeric argument as a repeat count, when
646 Because @key{TAB} serves as a completion command, you can't use it to
647 enter a tab as input to the program you are debugging with GDB.
648 Instead, type @kbd{C-q @key{TAB}} to enter a tab.
650 @node GUD Customization
651 @subsection GUD Customization
653 @vindex gdb-mode-hook
654 @vindex dbx-mode-hook
655 @vindex sdb-mode-hook
656 @vindex xdb-mode-hook
657 @vindex perldb-mode-hook
658 @vindex pdb-mode-hook
659 @vindex jdb-mode-hook
660 On startup, GUD runs one of the following hooks: @code{gdb-mode-hook},
661 if you are using GDB; @code{dbx-mode-hook}, if you are using DBX;
662 @code{sdb-mode-hook}, if you are using SDB; @code{xdb-mode-hook}, if you
663 are using XDB; @code{perldb-mode-hook}, for Perl debugging mode;
664 @code{pdb-mode-hook}, for PDB; @code{jdb-mode-hook}, for JDB. You can
665 use these hooks to define custom key bindings for the debugger
666 interaction buffer. @xref{Hooks}.
668 Here is a convenient way to define a command that sends a particular
669 command string to the debugger, and set up a key binding for it in the
670 debugger interaction buffer:
674 (gud-def @var{function} @var{cmdstring} @var{binding} @var{docstring})
677 This defines a command named @var{function} which sends
678 @var{cmdstring} to the debugger process, and gives it the documentation
679 string @var{docstring}. You can then use the command @var{function} in any
680 buffer. If @var{binding} is non-@code{nil}, @code{gud-def} also binds
681 the command to @kbd{C-c @var{binding}} in the GUD buffer's mode and to
682 @kbd{C-x C-a @var{binding}} generally.
684 The command string @var{cmdstring} may contain certain
685 @samp{%}-sequences that stand for data to be filled in at the time
686 @var{function} is called:
690 The name of the current source file. If the current buffer is the GUD
691 buffer, then the ``current source file'' is the file that the program
693 @c This said, ``the name of the file the program counter was in at the last breakpoint.''
694 @c But I suspect it is really the last stop file.
697 The number of the current source line. If the current buffer is the GUD
698 buffer, then the ``current source line'' is the line that the program
702 The text of the C lvalue or function-call expression at or adjacent to point.
705 The text of the hexadecimal address at or adjacent to point.
708 The numeric argument of the called function, as a decimal number. If
709 the command is used without a numeric argument, @samp{%p} stands for the
712 If you don't use @samp{%p} in the command string, the command you define
713 ignores any numeric argument.
716 @node GDB Graphical Interface
717 @subsection GDB Graphical Interface
719 By default, the command @code{gdb} starts GDB using a graphical
720 interface where you view and control the program's data using Emacs
721 windows. You can still interact with GDB through the GUD buffer, but
722 the point of this mode is that you can do it through menus and clicks,
723 without needing to know GDB commands. For example, you can click
724 @kbd{Mouse-1} on a line of the source buffer, in the fringe or display
725 margin, to set a breakpoint there. If a breakpoint already exists on
726 that line, this action will remove it
727 (@code{gdb-mouse-set-clear-breakpoint}). Where Emacs uses the margin
728 to display breakpoints, it is also possible to enable or disable them
729 when you click @kbd{Mouse-3} there
730 (@code{gdb-mouse-toggle--breakpoint}).
732 @vindex gud-gdb-command-name
734 You can also run GDB in text command mode, which creates a buffer
735 for input and output to GDB. To do this, set
736 @code{gud-gdb-command-name} to @code{"gdb --fullname"} or edit the
737 startup command in the minibuffer to say that. You need to do use
738 text command mode to run multiple debugging sessions within one Emacs
739 session. If you have customised @code{gud-gdb-command-name} in that
740 way, then you can use @kbd{M-x gdba} to invoke GDB in graphical mode.
743 * Layout:: Control the number of displayed buffers.
744 * Breakpoints Buffer:: A breakpoint control panel.
745 * Stack Buffer:: Select a frame from the call stack.
746 * Watch Expressions:: Monitor variable values in the speedbar.
747 * Other Buffers:: Input/output, locals, registers, assembler, threads
752 @subsubsection Layout
753 @cindex GDB User Interface layout
755 @findex gdb-many-windows
756 @vindex gdb-many-windows
758 If the variable @code{gdb-many-windows} is @code{nil} (the default
759 value) then gdb just pops up the GUD buffer unless the variable
760 @code{gdb-show-main} is non-@code{nil}. In this case it starts with
761 two windows: one displaying the GUD buffer and the other with the
762 source file with the main routine of the inferior.
764 If @code{gdb-many-windows} is non-@code{nil}, regardless of the value of
765 @code{gdb-show-main}, the layout below will appear unless
766 @code{gdb-use-inferior-io-buffer} is @code{nil}. In this case the
767 source buffer occupies the full width of the frame.
769 @multitable @columnfractions .5 .5
770 @item GUD buffer (I/O of GDB)
775 @tab Input/Output (of inferior) buffer
779 @tab Breakpoints buffer
782 To toggle this layout, do @kbd{M-x gdb-many-windows}.
784 @findex gdb-restore-windows
785 If you change the window layout, for example, while editing and
786 re-compiling your program, then you can restore it with the command
787 @code{gdb-restore-windows}.
789 You may also choose which additional buffers you want to display,
790 either in the same frame or a different one. Select GDB-windows or
791 GDB-Frames from the menu-bar under the heading GUD. If the menu-bar
792 is unavailable, type @code{M-x
793 gdb-display-@var{buffertype}-buffer} or @code{M-x
794 gdb-frame-@var{buffertype}-buffer} respectively, where @var{buffertype}
795 is the relevant buffer type e.g breakpoints.
797 When you finish debugging then kill the GUD buffer with @kbd{C-x k},
798 which will also kill all the buffers associated with the session.
799 However you need not do this if, after editing and re-compiling your
800 source code within Emacs, you wish continue debugging. When you
801 restart execution, GDB will automatically find your new executable.
802 Keeping the GUD buffer has the advantage of keeping the shell history
803 as well as GDB's breakpoints. You need to check, however, that the
804 breakpoints in the recently edited code are still where you want them.
806 @node Breakpoints Buffer
807 @subsubsection Breakpoints Buffer
809 The breakpoints buffer shows the existing breakpoints and watchpoints
810 (@pxref{Breakpoints,,, gdb, The GNU debugger}). It has three special
815 @kindex SPC @r{(GDB breakpoints buffer)}
816 @findex gdb-toggle-breakpoint
817 Enable/disable the breakpoint at the current line
818 (@code{gdb-toggle-breakpoint}). On a graphical display, this changes
819 the color of a bullet in the margin of the source buffer at the
820 relevant line. This is red when the breakpoint is enabled and grey
821 when it is disabled. Text-only terminals correspondingly display
822 a @samp{B} or @samp{b}.
825 @kindex d @r{(GDB breakpoints buffer)}
826 @findex gdb-delete-breakpoint
827 Delete the breakpoint at the current line (@code{gdb-delete-breakpoint}).
830 @kindex RET @r{(GDB breakpoints buffer)}
831 @findex gdb-goto-breakpoint
832 Display the file in the source buffer at the breakpoint specified at
833 the current line (@code{gdb-goto-breakpoint}). Alternatively, click
834 @kbd{Mouse-2} on the breakpoint that you wish to visit.
838 @subsubsection Stack Buffer
840 The stack buffer displays a @dfn{call stack}, with one line for each
841 of the nested subroutine calls (@dfn{stack frames}) now active in the
842 program. @xref{Backtrace,,info stack, gdb, The GNU debugger}.
844 The selected frame is displayed in reverse contrast. Move point to
845 any frame in the stack and type @key{RET} to select it (@code{gdb-frames-select})
846 and display the associated source in the source buffer. Alternatively,
847 click @kbd{Mouse-2} to make the selected frame become the current one.
848 If the locals buffer is displayed then its contents update to display
849 the variables that are local to the new frame.
851 @node Watch Expressions
852 @subsubsection Watch Expressions
853 @cindex Watching expressions in GDB
855 If you want to see how a variable changes each time your program stops
856 then place the cursor over the variable name and click on the watch
857 icon in the toolbar (@code{gud-watch}).
859 Each watch expression is displayed in the speedbar. Complex data
860 types, such as arrays, structures and unions are represented in a tree
861 format. To expand or contract a complex data type, click @kbd{Mouse-2}
862 on the tag to the left of the expression.
864 @kindex RET @r{(GDB speedbar)}
865 @findex gdb-var-delete
866 With the cursor over the root expression of a complex data type, type
867 @kbd{D} to delete it from the speedbar
868 (@code{gdb-var-delete}).
870 @findex gdb-edit-value
871 With the cursor over a simple data type or an element of a complex
872 data type which holds a value, type @key{RET} or click @kbd{Mouse-2} to edit
873 its value. A prompt for a new value appears in the mini-buffer
874 (@code{gdb-edit-value}).
876 If you set the variable @code{gdb-show-changed-values} to
877 non-@code{nil} (the default value), then Emacs will use
878 font-lock-warning-face to display values that have recently changed in
881 If you set the variable @code{gdb-use-colon-colon-notation} to a
882 non-@code{nil} value, then, in C, Emacs will use the
883 FUNCTION::VARIABLE format to display variables in the speedbar.
884 Since this does not work for variables defined in compound statements,
885 the default value is @code{nil}.
888 @subsubsection Other Buffers
891 @item Input/Output Buffer
892 If the variable @code{gdb-use-inferior-io-buffer} is non-@code{nil},
893 the executable program that is being debugged takes its input and
894 displays its output here. Some of the commands from shell mode are
895 available here. @xref{Shell Mode}.
898 The locals buffer displays the values of local variables of the
899 current frame for simple data types (@pxref{Frame Info,,, gdb, The GNU
902 Arrays and structures display their type only. You must display them
903 separately to examine their values. @ref{Watch Expressions}.
905 @item Registers Buffer
906 The registers buffer displays the values held by the registers
907 (@pxref{Registers,,, gdb, The GNU debugger}).
909 @item Assembler Buffer
910 The assembler buffer displays the current frame as machine code. An
911 overlay arrow points to the current instruction and you can set and
912 remove breakpoints as with the source buffer. Breakpoint icons also
913 appear in the fringe or margin.
917 The threads buffer displays a summary of all threads currently in your
918 program (@pxref{Threads,,, gdb, The GNU debugger}). Move point to
919 any thread in the list and type @key{RET} to make it become the
920 current thread (@code{gdb-threads-select}) and display the associated
921 source in the source buffer. Alternatively, click @kbd{Mouse-2} to
922 make the selected thread become the current one.
926 The memory buffer allows the user to examine sections of program
927 memory (@pxref{Memory,,, gdb, The GNU debugger}). Click @kbd{Mouse-1}
928 on the appropriate part of the header line to change the starting
929 address or number of data items that the buffer displays.
930 Click @kbd{Mouse-3} on the header line to select the display format
931 or unit size for these data items.
936 @section Executing Lisp Expressions
938 Emacs has several different major modes for Lisp and Scheme. They are
939 the same in terms of editing commands, but differ in the commands for
940 executing Lisp expressions. Each mode has its own purpose.
943 @item Emacs-Lisp mode
944 The mode for editing source files of programs to run in Emacs Lisp.
945 This mode defines @kbd{C-M-x} to evaluate the current defun.
946 @xref{Lisp Libraries}.
947 @item Lisp Interaction mode
948 The mode for an interactive session with Emacs Lisp. It defines
949 @kbd{C-j} to evaluate the sexp before point and insert its value in the
950 buffer. @xref{Lisp Interaction}.
952 The mode for editing source files of programs that run in Lisps other
953 than Emacs Lisp. This mode defines @kbd{C-M-x} to send the current defun
954 to an inferior Lisp process. @xref{External Lisp}.
955 @item Inferior Lisp mode
956 The mode for an interactive session with an inferior Lisp process.
957 This mode combines the special features of Lisp mode and Shell mode
958 (@pxref{Shell Mode}).
960 Like Lisp mode but for Scheme programs.
961 @item Inferior Scheme mode
962 The mode for an interactive session with an inferior Scheme process.
965 Most editing commands for working with Lisp programs are in fact
966 available globally. @xref{Programs}.
969 @section Libraries of Lisp Code for Emacs
971 @cindex loading Lisp code
973 Lisp code for Emacs editing commands is stored in files whose names
974 conventionally end in @file{.el}. This ending tells Emacs to edit them in
975 Emacs-Lisp mode (@pxref{Executing Lisp}).
978 To execute a file of Emacs Lisp code, use @kbd{M-x load-file}. This
979 command reads a file name using the minibuffer and then executes the
980 contents of that file as Lisp code. It is not necessary to visit the
981 file first; in any case, this command reads the file as found on disk,
982 not text in an Emacs buffer.
986 Once a file of Lisp code is installed in the Emacs Lisp library
987 directories, users can load it using @kbd{M-x load-library}. Programs can
988 load it by calling @code{load-library}, or with @code{load}, a more primitive
989 function that is similar but accepts some additional arguments.
991 @kbd{M-x load-library} differs from @kbd{M-x load-file} in that it
992 searches a sequence of directories and tries three file names in each
993 directory. Suppose your argument is @var{lib}; the three names are
994 @file{@var{lib}.elc}, @file{@var{lib}.el}, and lastly just
995 @file{@var{lib}}. If @file{@var{lib}.elc} exists, it is by convention
996 the result of compiling @file{@var{lib}.el}; it is better to load the
997 compiled file, since it will load and run faster.
999 If @code{load-library} finds that @file{@var{lib}.el} is newer than
1000 @file{@var{lib}.elc} file, it issues a warning, because it's likely that
1001 somebody made changes to the @file{.el} file and forgot to recompile
1004 Because the argument to @code{load-library} is usually not in itself
1005 a valid file name, file name completion is not available. Indeed, when
1006 using this command, you usually do not know exactly what file name
1010 The sequence of directories searched by @kbd{M-x load-library} is
1011 specified by the variable @code{load-path}, a list of strings that are
1012 directory names. The default value of the list contains the directory where
1013 the Lisp code for Emacs itself is stored. If you have libraries of
1014 your own, put them in a single directory and add that directory
1015 to @code{load-path}. @code{nil} in this list stands for the current default
1016 directory, but it is probably not a good idea to put @code{nil} in the
1017 list. If you find yourself wishing that @code{nil} were in the list,
1018 most likely what you really want to do is use @kbd{M-x load-file}
1022 Often you do not have to give any command to load a library, because
1023 the commands defined in the library are set up to @dfn{autoload} that
1024 library. Trying to run any of those commands calls @code{load} to load
1025 the library; this replaces the autoload definitions with the real ones
1029 Emacs Lisp code can be compiled into byte-code which loads faster,
1030 takes up less space when loaded, and executes faster. @xref{Byte
1031 Compilation,, Byte Compilation, elisp, the Emacs Lisp Reference Manual}.
1032 By convention, the compiled code for a library goes in a separate file
1033 whose name consists of the library source file with @samp{c} appended.
1034 Thus, the compiled code for @file{foo.el} goes in @file{foo.elc}.
1035 That's why @code{load-library} searches for @samp{.elc} files first.
1037 @vindex load-dangerous-libraries
1038 @cindex Lisp files byte-compiled by XEmacs
1039 By default, Emacs refuses to load compiled Lisp files which were
1040 compiled with XEmacs, a modified versions of Emacs---they can cause
1041 Emacs to crash. Set the variable @code{load-dangerous-libraries} to
1042 @code{t} if you want to try loading them.
1045 @section Evaluating Emacs Lisp Expressions
1046 @cindex Emacs-Lisp mode
1047 @cindex mode, Emacs-Lisp
1049 @findex emacs-lisp-mode
1050 Lisp programs intended to be run in Emacs should be edited in
1051 Emacs-Lisp mode; this happens automatically for file names ending in
1052 @file{.el}. By contrast, Lisp mode itself is used for editing Lisp
1053 programs intended for other Lisp systems. To switch to Emacs-Lisp mode
1054 explicitly, use the command @kbd{M-x emacs-lisp-mode}.
1056 For testing of Lisp programs to run in Emacs, it is often useful to
1057 evaluate part of the program as it is found in the Emacs buffer. For
1058 example, after changing the text of a Lisp function definition,
1059 evaluating the definition installs the change for future calls to the
1060 function. Evaluation of Lisp expressions is also useful in any kind of
1061 editing, for invoking noninteractive functions (functions that are
1066 Read a single Lisp expression in the minibuffer, evaluate it, and print
1067 the value in the echo area (@code{eval-expression}).
1069 Evaluate the Lisp expression before point, and print the value in the
1070 echo area (@code{eval-last-sexp}).
1072 Evaluate the defun containing or after point, and print the value in
1073 the echo area (@code{eval-defun}).
1074 @item M-x eval-region
1075 Evaluate all the Lisp expressions in the region.
1076 @item M-x eval-current-buffer
1077 Evaluate all the Lisp expressions in the buffer.
1081 @c This uses ``colon'' instead of a literal `:' because Info cannot
1082 @c cope with a `:' in a menu
1083 @kindex M-@key{colon}
1088 @findex eval-expression
1089 @kbd{M-:} (@code{eval-expression}) is the most basic command for evaluating
1090 a Lisp expression interactively. It reads the expression using the
1091 minibuffer, so you can execute any expression on a buffer regardless of
1092 what the buffer contains. When the expression is evaluated, the current
1093 buffer is once again the buffer that was current when @kbd{M-:} was
1096 @kindex C-M-x @r{(Emacs-Lisp mode)}
1098 In Emacs-Lisp mode, the key @kbd{C-M-x} is bound to the command
1099 @code{eval-defun}, which parses the defun containing or following point
1100 as a Lisp expression and evaluates it. The value is printed in the echo
1101 area. This command is convenient for installing in the Lisp environment
1102 changes that you have just made in the text of a function definition.
1104 @kbd{C-M-x} treats @code{defvar} expressions specially. Normally,
1105 evaluating a @code{defvar} expression does nothing if the variable it
1106 defines already has a value. But @kbd{C-M-x} unconditionally resets the
1107 variable to the initial value specified in the @code{defvar} expression.
1108 @code{defcustom} expressions are treated similarly.
1109 This special feature is convenient for debugging Lisp programs.
1110 Typing @kbd{C-M-x} on a @code{defface} expression reinitializes
1111 the face according to the @code{defface} specification.
1114 @findex eval-last-sexp
1115 The command @kbd{C-x C-e} (@code{eval-last-sexp}) evaluates the Lisp
1116 expression preceding point in the buffer, and displays the value in the
1117 echo area. It is available in all major modes, not just Emacs-Lisp
1118 mode. It does not treat @code{defvar} specially.
1120 When the result of an evaluation is an integer, you can type
1121 @kbd{C-x C-e} a second time to display the value of the integer result
1122 in additional formats (octal, hexadecimal, and character).
1124 If @kbd{C-M-x}, @kbd{C-x C-e}, or @kbd{M-:} is given a numeric
1125 argument, it inserts the value into the current buffer at point, rather
1126 than displaying it in the echo area. The argument's value does not
1130 @findex eval-current-buffer
1131 The most general command for evaluating Lisp expressions from a buffer
1132 is @code{eval-region}. @kbd{M-x eval-region} parses the text of the
1133 region as one or more Lisp expressions, evaluating them one by one.
1134 @kbd{M-x eval-current-buffer} is similar but evaluates the entire
1135 buffer. This is a reasonable way to install the contents of a file of
1136 Lisp code that you are ready to test. Later, as you find bugs and
1137 change individual functions, use @kbd{C-M-x} on each function that you
1138 change. This keeps the Lisp world in step with the source file.
1140 @vindex eval-expression-print-level
1141 @vindex eval-expression-print-length
1142 @vindex eval-expression-debug-on-error
1143 The customizable variables @code{eval-expression-print-level} and
1144 @code{eval-expression-print-length} control the maximum depth and length
1145 of lists to print in the result of the evaluation commands before
1146 abbreviating them. @code{eval-expression-debug-on-error} controls
1147 whether evaluation errors invoke the debugger when these commands are
1150 @node Lisp Interaction
1151 @section Lisp Interaction Buffers
1153 The buffer @samp{*scratch*} which is selected when Emacs starts up is
1154 provided for evaluating Lisp expressions interactively inside Emacs.
1156 The simplest way to use the @samp{*scratch*} buffer is to insert Lisp
1157 expressions and type @kbd{C-j} after each expression. This command
1158 reads the Lisp expression before point, evaluates it, and inserts the
1159 value in printed representation before point. The result is a complete
1160 typescript of the expressions you have evaluated and their values.
1162 The @samp{*scratch*} buffer's major mode is Lisp Interaction mode, which
1163 is the same as Emacs-Lisp mode except for the binding of @kbd{C-j}.
1165 @findex lisp-interaction-mode
1166 The rationale for this feature is that Emacs must have a buffer when
1167 it starts up, but that buffer is not useful for editing files since a
1168 new buffer is made for every file that you visit. The Lisp interpreter
1169 typescript is the most useful thing I can think of for the initial
1170 buffer to do. Type @kbd{M-x lisp-interaction-mode} to put the current
1171 buffer in Lisp Interaction mode.
1174 An alternative way of evaluating Emacs Lisp expressions interactively
1175 is to use Inferior Emacs-Lisp mode, which provides an interface rather
1176 like Shell mode (@pxref{Shell Mode}) for evaluating Emacs Lisp
1177 expressions. Type @kbd{M-x ielm} to create an @samp{*ielm*} buffer
1178 which uses this mode.
1181 @section Running an External Lisp
1183 Emacs has facilities for running programs in other Lisp systems. You can
1184 run a Lisp process as an inferior of Emacs, and pass expressions to it to
1185 be evaluated. You can also pass changed function definitions directly from
1186 the Emacs buffers in which you edit the Lisp programs to the inferior Lisp
1190 @vindex inferior-lisp-program
1192 To run an inferior Lisp process, type @kbd{M-x run-lisp}. This runs
1193 the program named @code{lisp}, the same program you would run by typing
1194 @code{lisp} as a shell command, with both input and output going through
1195 an Emacs buffer named @samp{*lisp*}. That is to say, any ``terminal
1196 output'' from Lisp will go into the buffer, advancing point, and any
1197 ``terminal input'' for Lisp comes from text in the buffer. (You can
1198 change the name of the Lisp executable file by setting the variable
1199 @code{inferior-lisp-program}.)
1201 To give input to Lisp, go to the end of the buffer and type the input,
1202 terminated by @key{RET}. The @samp{*lisp*} buffer is in Inferior Lisp
1203 mode, which combines the special characteristics of Lisp mode with most
1204 of the features of Shell mode (@pxref{Shell Mode}). The definition of
1205 @key{RET} to send a line to a subprocess is one of the features of Shell
1209 For the source files of programs to run in external Lisps, use Lisp
1210 mode. This mode can be selected with @kbd{M-x lisp-mode}, and is used
1211 automatically for files whose names end in @file{.l}, @file{.lsp}, or
1212 @file{.lisp}, as most Lisp systems usually expect.
1214 @kindex C-M-x @r{(Lisp mode)}
1215 @findex lisp-eval-defun
1216 When you edit a function in a Lisp program you are running, the easiest
1217 way to send the changed definition to the inferior Lisp process is the key
1218 @kbd{C-M-x}. In Lisp mode, this runs the function @code{lisp-eval-defun},
1219 which finds the defun around or following point and sends it as input to
1220 the Lisp process. (Emacs can send input to any inferior process regardless
1221 of what buffer is current.)
1223 Contrast the meanings of @kbd{C-M-x} in Lisp mode (for editing programs
1224 to be run in another Lisp system) and Emacs-Lisp mode (for editing Lisp
1225 programs to be run in Emacs): in both modes it has the effect of installing
1226 the function definition that point is in, but the way of doing so is
1227 different according to where the relevant Lisp environment is found.
1228 @xref{Executing Lisp}.
1231 arch-tag: 9c3c2f71-b332-4144-8500-3ff9945a50ed