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The previous chapter discusses the Emacs commands that are useful for making changes in programs. This chapter deals with commands that assist in the larger process of compiling and testing programs.
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Emacs can run compilers for noninteractive languages such as C and Fortran as inferior processes, feeding the error log into an Emacs buffer. It can also parse the error messages and show you the source lines where compilation errors occurred.
Run a compiler asynchronously under Emacs, with error messages going to the `*compilation*' buffer.
Invoke a compiler with the same command as in the last invocation of M-x compile.
Kill the running compilation subprocess.
To run make or another compilation command, do M-x
compile. This command reads a shell command line using the minibuffer,
and then executes the command in an inferior shell, putting output in
the buffer named `*compilation*'. The current buffer's default
directory is used as the working directory for the execution of the
command; normally, therefore, the compilation happens in this
directory.
The default for the compilation command is normally `make -k',
which is correct most of the time for nontrivial programs.
(See (make)Top section `Make' in GNU Make Manual.) If you have done M-x
compile before, the default each time is the command you used the
previous time. compile stores this command in the variable
compile-command, so setting that variable specifies the default
for the next use of M-x compile. If a file specifies a file
local value for compile-command, that provides the default when
you type M-x compile in that file's buffer. See section Local Variables in Files.
Starting a compilation displays the buffer `*compilation*' in another window but does not select it. The buffer's mode line tells you whether compilation is finished, with the word `run', `signal' or `exit' inside the parentheses. You do not have to keep this buffer visible; compilation continues in any case. While a compilation is going on, the string `Compiling' appears in the mode lines of all windows. When this string disappears, the compilation is finished.
If you want to watch the compilation transcript as it appears, switch to the `*compilation*' buffer and move point to the end of the buffer. When point is at the end, new compilation output is inserted above point, which remains at the end. If point is not at the end of the buffer, it remains fixed while more compilation output is added at the end of the buffer.
If you set the variable compilation-scroll-output to a
non-nil value, then the compilation buffer always scrolls to
follow output as it comes in.
To rerun the last compilation with the same command, type M-x recompile. This automatically reuses the compilation command from the last invocation of M-x compile. It also reuses the `*compilation*' buffer and starts the compilation in its default directory, which is the directory in which the previous compilation was started.
When the compiler process terminates, for whatever reason, the mode line of the `*compilation*' buffer changes to say `exit' (followed by the exit code, `[0]' for a normal exit), or `signal' (if a signal terminated the process), instead of `run'.
Starting a new compilation also kills any compilation already running in `*compilation*', as the buffer can only handle one compilation at any time. However, M-x compile asks for confirmation before actually killing a compilation that is running. You can also kill the compilation process with M-x kill-compilation.
If you want to run two compilations at once, you should start the
first one, then rename the `*compilation*' buffer (perhaps using
rename-uniquely; see section Miscellaneous Buffer Operations), and start the other
compilation. That will create a new `*compilation*' buffer.
Emacs does not expect a compiler process to launch asynchronous subprocesses; if it does, and they keep running after the main compiler process has terminated, Emacs may kill them or their output may not arrive in Emacs. To avoid this problem, make the main process wait for its subprocesses to finish. In a shell script, you can do this using `$!' and `wait', like this:
(sleep 10; echo 2nd)& pid=$! # Record pid of subprocess echo first message wait $pid # Wait for subprocess |
If the background process does not output to the compilation buffer, so you only need to prevent it from being killed when the main compilation process terminates, this is sufficient:
nohup command; sleep 1 |
You can control the environment passed to the compilation command
with the variable compilation-environment. Its value is a list
of environment variable settings; each element should be a string of
the form "envvarname=value". These environment
variable settings override the usual ones.
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The `*compilation*' buffer uses a special major mode, Compilation mode, whose main feature is to provide a convenient way to visit the source line corresponding to an error message. These commands are also available in other special buffers that list locations in files, including those made by M-x grep and M-x occur.
Visit the locus of the next error message or match.
Visit the locus of the previous error message or match.
Visit the locus of the error message that point is on. This command is used in the compilation buffer.
Visit the locus of the error message that you click on.
Find and highlight the locus of the next error message, without selecting the source buffer.
Find and highlight the locus of the previous error message, without selecting the source buffer.
Move point to the next error for a different file than the current one.
Move point to the previous error for a different file than the current one.
Toggle Next Error Follow minor mode, which makes cursor motion in the compilation buffer produce automatic source display.
You can visit the source for any particular error message by moving
point in the `*compilation*' buffer to that error message and
typing RET (compile-goto-error). Alternatively, you can
click Mouse-2 on the error message; you need not switch to the
`*compilation*' buffer first.
To parse the compiler error messages sequentially, type C-x `
(next-error). The character following the C-x is the
backquote or "grave accent," not the single-quote. This command is
available in all buffers, not just in `*compilation*'; it
displays the next error message at the top of one window and source
location of the error in another window. It also temporarily
highlights the relevant source line, for a period controlled by the
variable next-error-highlight.
The first time C-x ` is used after the start of a compilation, it moves to the first error's location. Subsequent uses of C-x ` advance down to subsequent errors. If you visit a specific error message with RET or Mouse-2, subsequent C-x ` commands advance from there. When C-x ` gets to the end of the buffer and finds no more error messages to visit, it fails and signals an Emacs error. C-u C-x ` starts scanning from the beginning of the compilation buffer, and goes to the first error's location.
By default, C-x ` skips less important messages. The variable
compilation-skip-threshold controls this. If its value is 2,
C-x ` skips anything less than error, 1 skips anything less
than warning, and 0 doesn't skip any messages. The default is 1.
When the window has a left fringe, an arrow in the fringe points to
the current message in the compilation buffer. The variable
compilation-context-lines controls the number of lines of
leading context to display before the current message. Going to an
error message location scrolls the `*compilation*' buffer to put
the message that far down from the top. The value nil is
special: if there's a left fringe, the window doesn't scroll at all
if the message is already visible. If there is no left fringe,
nil means display the message at the top of the window.
If you're not in the compilation buffer when you run
next-error, Emacs will look for a buffer that contains error
messages. First, it looks for one displayed in the selected frame,
then for one that previously had next-error called on it, and
then at the current buffer. Finally, Emacs looks at all the remaining
buffers. next-error signals an error if it can't find any such
buffer.
To parse messages from the compiler, Compilation mode uses the
variable compilation-error-regexp-alist which lists various
formats of error messages and tells Emacs how to extract the source file
and the line number from the text of a message. If your compiler isn't
supported, you can tailor Compilation mode to it by adding elements to
that list. A similar variable grep-regexp-alist tells Emacs how
to parse output of a grep command.
Compilation mode also redefines the keys SPC and DEL to
scroll by screenfuls, and M-n (compilation-next-error)
and M-p (compilation-previous-error) to move to the next
or previous error message. You can also use M-{
(compilation-next-file and M-}
(compilation-previous-file) to move up or down to an error
message for a different source file.
You can type C-c C-f to toggle Next Error Follow mode. In this minor mode, ordinary cursor motion in the compilation buffer automatically updates the source buffer. For instance, moving the cursor to the next error message causes the location of that error to be displayed immediately.
The features of Compilation mode are also available in a minor mode called Compilation Minor mode. This lets you parse error messages in any buffer, not just a normal compilation output buffer. Type M-x compilation-minor-mode to enable the minor mode. This defines the keys RET and Mouse-2, as in the Compilation major mode.
Compilation minor mode works in any buffer, as long as the contents are in a format that it understands. In an Rlogin buffer (see section Remote Host Shell), Compilation minor mode automatically accesses remote source files by FTP (see section File Names).
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Emacs uses a shell to run the compilation command, but specifies the option for a noninteractive shell. This means, in particular, that the shell should start with no prompt. If you find your usual shell prompt making an unsightly appearance in the `*compilation*' buffer, it means you have made a mistake in your shell's init file by setting the prompt unconditionally. (This init file's name may be `.bashrc', `.profile', `.cshrc', `.shrc', or various other things, depending on the shell you use.) The shell init file should set the prompt only if there already is a prompt. Here's how to do it in bash:
if [ "${PS1+set}" = set ]
then PS1=…
fi
|
And here's how to do it in csh:
if ($?prompt) set prompt = … |
There may well be other things that your shell's init file ought to do only for an interactive shell. You can use the same method to conditionalize them.
The MS-DOS "operating system" does not support asynchronous subprocesses; to work around this lack, M-x compile runs the compilation command synchronously on MS-DOS. As a consequence, you must wait until the command finishes before you can do anything else in Emacs. See section Emacs and MS-DOS.
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Just as you can run a compiler from Emacs and then visit the lines
with compilation errors, you can also run grep and then visit
the lines on which matches were found. This works by treating the
matches reported by grep as if they were "errors." The
buffer of matches uses Grep mode, which is a variant of Compilation
mode (see section Compilation Mode).
Run grep asynchronously under Emacs, with matching lines
listed in the buffer named `*grep*'.
Run grep via find, with user-specified arguments, and
collect output in the buffer named `*grep*'.
Kill the running grep subprocess.
To run grep, type M-x grep, then enter a command line
that specifies how to run grep. Use the same arguments you
would give grep when running it normally: a grep-style
regexp (usually in single-quotes to quote the shell's special
characters) followed by file names, which may use wildcards. If you
specify a prefix argument for M-x grep, it finds the tag
(see section Tags Tables) in the buffer around point, and puts that into the
default grep command.
Your command need not simply run grep; you can use any shell
command that produces output in the same format. For instance, you
can chain grep commands, like this:
grep -nH -e foo *.el | grep bar | grep toto |
The output from grep goes in the `*grep*' buffer. You
can find the corresponding lines in the original files using C-x
`, RET, and so forth, just like compilation errors.
Some grep programs accept a `--color' option to output special
markers around matches for the purpose of highlighting. You can make
use of this feature by setting grep-highlight-matches to
t. When displaying a match in the source buffer, the exact
match will be highlighted, instead of the entire source line.
The command M-x grep-find (also available as M-x
find-grep) is similar to M-x grep, but it supplies a different
initial default for the command--one that runs both find and
grep, so as to search every file in a directory tree. See also
the find-grep-dired command, in Dired and find.
The commands M-x lgrep (local grep) and M-x rgrep
(recursive grep) are more user-friendly versions of grep and
grep-find, which prompt separately for the regular expression
to match, the files to search, and the base directory for the search.
Case sensitivity of the search is controlled by the
current value of case-fold-search.
These commands build the shell commands based on the variables
grep-template (for lgrep) and grep-find-template
(for rgrep).
The files to search can use aliases defined in the variable
grep-files-aliases.
Subdirectories listed in the variable
grep-find-ignored-directories such as those typically used by
various version control systems, like CVS and arch, are automatically
skipped by rgrep.
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Flymake mode is a minor mode that performs on-the-fly syntax
checking for many programming and markup languages, including C, C++,
Perl, HTML, and TeX/LaTeX. It is somewhat analogous to Flyspell
mode, which performs spell checking for ordinary human languages in a
similar fashion (see section Checking and Correcting Spelling). As you edit a file, Flymake mode
runs an appropriate syntax checking tool in the background, using a
temporary copy of the buffer. It then parses the error and warning
messages, and highlights the erroneous lines in the buffer. The
syntax checking tool used depends on the language; for example, for
C/C++ files this is usually the C compiler. Flymake can also use
build tools such as make for checking complicated projects.
To activate Flymake mode, type M-x flymake-mode. You can move to the errors spotted by Flymake mode with M-x flymake-goto-next-error and M-x flymake-goto-prev-error. To display any error messages associated with the current line, use M-x flymake-display-err-menu-for-current-line.
For more details about using Flymake, see Flymake: (flymake)Top section `Flymake' in The Flymake Manual.
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The GUD (Grand Unified Debugger) library provides an interface to various symbolic debuggers from within Emacs. We recommend the debugger GDB, which is free software, but GUD can also run DBX, SDB or XDB. GUD can also serve as an interface to Perl's debugging mode, the Python debugger PDB, and to JDB, the Java Debugger. See (elisp)Debugging section `The Lisp Debugger' in the Emacs Lisp Reference Manual, for information on debugging Emacs Lisp programs.
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There are several commands for starting a debugger, each corresponding to a particular debugger program.
Run GDB as a subprocess of Emacs. By default, this uses an IDE-like graphical interface; see GDB Graphical Interface. Only GDB works with the graphical interface.
Run DBX as a subprocess of Emacs. Since Emacs does not implement a graphical interface for DBX, communication with DBX works by typing commands in the GUD interaction buffer. The same is true for all the other supported debuggers.
Similar, but run XDB. Use the variable
gud-xdb-directories to specify directories to search for source
files.
Similar, but run SDB.
Some versions of SDB do not mention source file names in their messages. When you use them, you need to have a valid tags table (see section Tags Tables) in order for GUD to find functions in the source code. If you have not visited a tags table or the tags table doesn't list one of the functions, you get a message saying `The sdb support requires a valid tags table to work'. If this happens, generate a valid tags table in the working directory and try again.
Run the Perl interpreter in debug mode to debug file, a Perl program.
Run the Java debugger to debug file.
Run the Python debugger to debug file.
Each of these commands takes one argument: a command line to invoke the debugger. In the simplest case, specify just the name of the executable file you want to debug. You may also use options that the debugger supports. However, shell wildcards and variables are not allowed. GUD assumes that the first argument not starting with a `-' is the executable file name.
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Generally when you run a debugger with GUD, the debugger uses an Emacs buffer for its ordinary input and output. This is called the GUD buffer. Input and output from the program you are debugging also use this buffer. We call this text command mode. The GDB Graphical Interface can use further buffers (see section GDB Graphical Interface).
The debugger displays the source files of the program by visiting them in Emacs buffers. An arrow in the left fringe indicates the current execution line.(16) Moving point in this buffer does not move the arrow. The arrow is not part of the file's text; it appears only on the screen.
You can start editing these source files at any time in the buffers that display them. If you do modify a source file, keep in mind that inserting or deleting lines will throw off the arrow's positioning; GUD has no way of figuring out which line corresponded before your changes to the line number in a debugger message. Also, you'll typically have to recompile and restart the program for your changes to be reflected in the debugger's tables.
The Tooltip facility (see section Tooltips) provides support for GUD.
You activate this feature by turning on the minor mode
gud-tooltip-mode. Then you can display a variable's value in a
tooltip simply by pointing at it with the mouse. This operates in the
GUD buffer and in source buffers with major modes in the list
gud-tooltip-modes. If the variable gud-tooltip-echo-area
is non-nil then the variable's value is displayed in the echo
area. When debugging a C program using the GDB Graphical Interface, you
can also display macro definitions associated with an identifier when
the program is not executing.
GUD tooltips are disabled when you use GDB in text command mode (see section GDB Graphical Interface), because displaying an expression's value in GDB can sometimes expand a macro and result in a side effect that interferes with the program's operation. The GDB graphical interface supports GUD tooltips and assures they will not cause side effects.
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The GUD interaction buffer uses a variant of Shell mode, so the Emacs commands of Shell mode are available (see section Shell Mode). All the usual commands for your debugger are available, and you can use the Shell mode history commands to repeat them. If you wish, you can control your debugger process entirely through this buffer.
GUD mode also provides commands for setting and clearing
breakpoints, for selecting stack frames, and for stepping through the
program. These commands are available both in the GUD buffer and
globally, but with different key bindings. It also has its own tool
bar from which you can invoke the more common commands by clicking on
the appropriate icon. This is particularly useful for repetitive
commands like gud-next and gud-step, and allows you to
keep the GUD buffer hidden.
The breakpoint commands are normally used in source file buffers, because that is the easiest way to specify where to set or clear the breakpoint. Here's the global command to set a breakpoint:
Set a breakpoint on the source line that point is on.
Here are the other special commands provided by GUD. The keys starting with C-c are available only in the GUD interaction buffer. The key bindings that start with C-x C-a are available in the GUD interaction buffer and also in source files. Some of these commands are not available to all the supported debuggers.
Display in another window the last line referred to in the GUD
buffer (that is, the line indicated in the last location message).
This runs the command gud-refresh.
Execute a single line of code (gud-step). If the line contains
a function call, execution stops after entering the called function.
Execute a single line of code, stepping across entire function calls
at full speed (gud-next).
Execute a single machine instruction (gud-stepi).
Evaluate the expression at point (gud-print). If Emacs
does not print the exact expression that you want, mark it as a region
first.
Continue execution without specifying any stopping point. The program
will run until it hits a breakpoint, terminates, or gets a signal that
the debugger is checking for (gud-cont).
Delete the breakpoint(s) on the current source line, if any
(gud-remove). If you use this command in the GUD interaction
buffer, it applies to the line where the program last stopped.
Set a temporary breakpoint on the current source line, if any
(gud-tbreak). If you use this command in the GUD interaction
buffer, it applies to the line where the program last stopped.
Select the next enclosing stack frame (gud-up). This is
equivalent to the GDB command `up'.
Select the next inner stack frame (gud-down). This is
equivalent to the GDB command `down'.
Continue execution to the current line (gud-until). The
program will run until it hits a breakpoint, terminates, gets a signal
that the debugger is checking for, or reaches the line on which the
cursor currently sits.
Run the program until the selected stack frame returns or
stops for some other reason (gud-finish).
If you are using GDB, these additional key bindings are available:
Only useful in a source buffer, gud-jump transfers the
program's execution point to the current line. In other words, the
next line that the program executes will be the one where you gave the
command. If the new execution line is in a different function from
the previously one, GDB prompts for confirmation since the results may
be bizarre. See the GDB manual entry regarding jump for
details.
With GDB, complete a symbol name (gud-gdb-complete-command).
This key is available only in the GUD interaction buffer.
These commands interpret a numeric argument as a repeat count, when that makes sense.
Because TAB serves as a completion command, you can't use it to enter a tab as input to the program you are debugging with GDB. Instead, type C-q TAB to enter a tab.
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On startup, GUD runs one of the following hooks: gdb-mode-hook,
if you are using GDB; dbx-mode-hook, if you are using DBX;
sdb-mode-hook, if you are using SDB; xdb-mode-hook, if you
are using XDB; perldb-mode-hook, for Perl debugging mode;
pdb-mode-hook, for PDB; jdb-mode-hook, for JDB. You can
use these hooks to define custom key bindings for the debugger
interaction buffer. See section Hooks.
Here is a convenient way to define a command that sends a particular command string to the debugger, and set up a key binding for it in the debugger interaction buffer:
(gud-def function cmdstring binding docstring) |
This defines a command named function which sends
cmdstring to the debugger process, and gives it the documentation
string docstring. You can then use the command function in any
buffer. If binding is non-nil, gud-def also binds
the command to C-c binding in the GUD buffer's mode and to
C-x C-a binding generally.
The command string cmdstring may contain certain `%'-sequences that stand for data to be filled in at the time function is called:
The name of the current source file. If the current buffer is the GUD buffer, then the "current source file" is the file that the program stopped in.
The number of the current source line. If the current buffer is the GUD buffer, then the "current source line" is the line that the program stopped in.
In transient-mark-mode the text in the region, if it is active. Otherwise the text of the C lvalue or function-call expression at or adjacent to point.
The text of the hexadecimal address at or adjacent to point.
The numeric argument of the called function, as a decimal number. If the command is used without a numeric argument, `%p' stands for the empty string.
If you don't use `%p' in the command string, the command you define ignores any numeric argument.
The name of the directory of the current source file.
Fully qualified class name derived from the expression surrounding point (jdb only).
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By default, the command gdb starts GDB using a graphical
interface, using Emacs windows for display program state information.
In effect, this makes Emacs into an IDE (interactive development
environment). With it, you do not need to use textual GDB commands;
you can control the debugging session with the mouse. For example,
you can click in the fringe of a source buffer to set a breakpoint
there, or on a stack frame in the stack buffer to select that frame.
This mode requires telling GDB that its "screen size" is unlimited, so it sets the height and width accordingly. For correct operation you must not change these values during the GDB session.
You can also run GDB in text command mode, like other debuggers. To
do this, replace the GDB "--annotate=3" option with
"--fullname" either in the minibuffer for the current Emacs
session, or the custom variable gud-gdb-command-name for all
future sessions. You need to use text command mode to debug multiple
programs within one Emacs session. If you have customized
gud-gdb-command-name in this way, you can use M-x gdba to
invoke GDB in graphical mode.
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If the variable gdb-many-windows is nil (the default
value) then M-x gdb normally displays only the GUD buffer.
However, if the variable gdb-show-main is also non-nil,
it starts with two windows: one displaying the GUD buffer, and the
other showing the source for the main function of the program
you are debugging.
If gdb-many-windows is non-nil, then M-x gdb
displays the following frame layout:
+--------------------------------+--------------------------------+ | GUD buffer (I/O of GDB) | Locals buffer | |--------------------------------+--------------------------------+ | Primary Source buffer | I/O buffer for debugged pgm | |--------------------------------+--------------------------------+ | Stack buffer | Breakpoints buffer | +--------------------------------+--------------------------------+ |
However, if gdb-use-separate-io-buffer is nil, the I/O
buffer does not appear and the primary source buffer occupies the full
width of the frame.
If you change the window layout, for example, while editing and
re-compiling your program, then you can restore this standard window
layout with the command gdb-restore-windows.
To switch between this standard layout and a simple layout containing just the GUD buffer and a source file, type M-x gdb-many-windows.
You may also specify additional GDB-related buffers to display,
either in the same frame or a different one. Select the buffers you
want with the `GUD->GDB-windows' and `GUD->GDB-Frames'
sub-menus. If the menu-bar is unavailable, type M-x
gdb-display-buffertype-buffer or M-x
gdb-frame-buffertype-buffer respectively, where
buffertype is the relevant buffer type, such as
`breakpoints'. Most of these buffers are read-only, and typing
q in them kills them.
When you finish debugging, kill the GUD buffer with C-x k, which will also kill all the buffers associated with the session. However you need not do this if, after editing and re-compiling your source code within Emacs, you wish continue debugging. When you restart execution, GDB will automatically find your new executable. Keeping the GUD buffer has the advantage of keeping the shell history as well as GDB's breakpoints. You do need to check that the breakpoints in recently edited source files are still in the right places.
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Many GDB commands can be entered using keybindings or the tool bar but sometimes it is quicker to use the fringe. These commands either manipulate breakpoints or control program execution. When there is no fringe, you can use the margin but this is only present when the source file already has a breakpoint.
You can click Mouse-1 in the fringe or display margin of a source buffer to set a breakpoint there and, on a graphical display, a red bullet will appear on that line. If a breakpoint already exists on that line, the same click will remove it. You can also enable or disable a breakpoint by clicking C-Mouse-1 on the bullet.
A solid arrow in the left fringe of a source buffer indicates the line of the innermost frame where the debugged program has stopped. A hollow arrow indicates the current execution line of higher level frames.
If you drag the arrow in the fringe with Mouse-1
(gdb-mouse-until), execution will continue to the line where
you release the button, provided it is still in the same frame.
Alternatively, you can click Mouse-3 at some point in the fringe
of this buffer and execution will advance to there. A similar command
(gdb-mouse-jump) allows you to jump to a source line without
executing the intermediate lines by clicking C-Mouse-3. This
command allows you to go backwards which can be useful for running
through code that has already executed, in order to examine its
execution in more detail.
Set or clear a breakpoint.
Enable or disable a breakpoint.
Continue execution to here.
Jump to here.
If the variable gdb-find-source-frame is non-nil and
execution stops in a frame for which there is no source code e.g after
an interrupt, then Emacs finds and displays the first frame further up
stack for which there is source. If it is nil then the source
buffer continues to display the last frame which maybe more useful,
for example, when re-setting a breakpoint.
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The breakpoints buffer shows the existing breakpoints, watchpoints and catchpoints (see (gdb)Breakpoints section `Breakpoints' in The GNU debugger). It has these special commands, which mostly apply to the current breakpoint, the breakpoint which point is on.
Enable/disable the current breakpoint (gdb-toggle-breakpoint).
On a graphical display, this changes the color of a bullet in the
margin of a source buffer at the relevant line. This is red when
the breakpoint is enabled and grey when it is disabled. Text-only
terminals correspondingly display a `B' or `b'.
Delete the current breakpoint (gdb-delete-breakpoint).
Visit the source line for the current breakpoint
(gdb-goto-breakpoint).
Visit the source line for the breakpoint you click on.
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The stack buffer displays a call stack, with one line for each of the nested subroutine calls (stack frames) now active in the program. See (gdb)Backtrace section `Backtraces' in The GNU debugger.
An arrow in the fringe points to the selected frame or, if the fringe is
not present, the number of the selected frame is displayed in reverse
contrast. To select a frame in GDB, move point in the stack buffer to
that stack frame and type RET (gdb-frames-select), or click
Mouse-2 on a stack frame. If the locals buffer is visible,
selecting a stack frame updates it to display the local variables of the
new frame.
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If the variable gdb-use-separate-io-buffer is non-nil,
the program being debugged takes its input and displays its output
here. Otherwise it uses the GUD buffer for that. To toggle whether
GUD mode uses this buffer, do M-x gdb-use-separate-io-buffer.
This takes effect when you next restart the program you are debugging.
The history and replay commands from Shell mode are available here, as are the commands to send signals to the debugged program. See section Shell Mode.
The locals buffer displays the values of local variables of the current frame for simple data types (see Frame Info: (gdb)Frame Info section `Information on a frame' in The GNU debugger). Press RET or click Mouse-2 on the value if you want to edit it.
Arrays and structures display their type only. With GDB 6.4 or later, move point to their name and press RET, or alternatively click Mouse-2 there, to examine their values. With earlier versions of GDB, use Mouse-2 or RET on the type description (`[struct/union]' or `[array]'). See section Watch Expressions.
The registers buffer displays the values held by the registers
(see (gdb)Registers section `Registers' in The GNU debugger). Press RET or
click Mouse-2 on a register if you want to edit its value.
With GDB 6.4 or later, recently changed register values display with
font-lock-warning-face. With earlier versions of GDB, you can
press SPC to toggle the display of floating point registers
(toggle-gdb-all-registers).
The assembler buffer displays the current frame as machine code. An arrow points to the current instruction, and you can set and remove breakpoints as in a source buffer. Breakpoint icons also appear in the fringe or margin.
The threads buffer displays a summary of all threads currently in your
program (see Threads: (gdb)Threads section `Debugging programs with multiple threads' in The GNU debugger). Move point to any thread in the
list and press RET to select it (gdb-threads-select) and
display the associated source in the primary source buffer.
Alternatively, click Mouse-2 on a thread to select it. If the
locals buffer is visible, its contents update to display the variables
that are local in the new thread.
The memory buffer lets you examine sections of program memory (see Memory: (gdb)Memory section `Examining memory' in The GNU debugger). Click Mouse-1 on the appropriate part of the header line to change the starting address or number of data items that the buffer displays. Click Mouse-3 on the header line to select the display format or unit size for these data items.
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If you want to see how a variable changes each time your program
stops, move point into the variable name and click on the watch icon
in the tool bar (gud-watch) or type C-x C-a C-w. If you
specify a prefix argument, you can enter the variable name in the
minibuffer.
Each watch expression is displayed in the speedbar. Complex data types, such as arrays, structures and unions are represented in a tree format. Leaves and simple data types show the name of the expression and its value and, when the speedbar frame is selected, display the type as a tooltip. Higher levels show the name, type and address value for pointers and just the name and type otherwise. Root expressions also display the frame address as a tooltip to help identify the frame in which they were defined.
To expand or contract a complex data type, click Mouse-2 or
press SPC on the tag to the left of the expression. Emacs asks
for confirmation before expanding the expression if its number of
immediate children exceeds the value of the variable
gdb-max-children.
To delete a complex watch expression, move point to the root
expression in the speedbar and type D (gdb-var-delete).
To edit a variable with a simple data type, or a simple element of a
complex data type, move point there in the speedbar and type RET
(gdb-edit-value). Or you can click Mouse-2 on a value to
edit it. Either way, this reads the new value using the minibuffer.
If you set the variable gdb-show-changed-values to
non-nil (the default value), Emacs uses
font-lock-warning-face to highlight values that have recently
changed and shadow face to make variables which have gone out of
scope less noticeable. When a variable goes out of scope you can't
edit its value.
If the variable gdb-use-colon-colon-notation is
non-nil, Emacs uses the `function::variable'
format. This allows the user to display watch expressions which share
the same variable name. The default value is nil.
To automatically raise the speedbar every time the display of watch
expressions updates, set gdb-speedbar-auto-raise to
non-nil. This can be useful if you are debugging with a full
screen Emacs frame.
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Emacs has several different major modes for Lisp and Scheme. They are the same in terms of editing commands, but differ in the commands for executing Lisp expressions. Each mode has its own purpose.
The mode for editing source files of programs to run in Emacs Lisp. This mode defines C-M-x to evaluate the current defun. See section Libraries of Lisp Code for Emacs.
The mode for an interactive session with Emacs Lisp. It defines C-j to evaluate the sexp before point and insert its value in the buffer. See section Lisp Interaction Buffers.
The mode for editing source files of programs that run in Lisps other than Emacs Lisp. This mode defines C-M-x to send the current defun to an inferior Lisp process. See section Running an External Lisp.
The mode for an interactive session with an inferior Lisp process. This mode combines the special features of Lisp mode and Shell mode (see section Shell Mode).
Like Lisp mode but for Scheme programs.
The mode for an interactive session with an inferior Scheme process.
Most editing commands for working with Lisp programs are in fact available globally. See section Editing Programs.
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Lisp code for Emacs editing commands is stored in files whose names conventionally end in `.el'. This ending tells Emacs to edit them in Emacs-Lisp mode (see section Executing Lisp Expressions).
Emacs Lisp code can be compiled into byte-code, which loads faster, takes up less space, and executes faster. See (elisp)Byte Compilation section `Byte Compilation' in the Emacs Lisp Reference Manual. By convention, the compiled code for a library goes in a separate file whose name ends in `.elc'. Thus, the compiled code for `foo.el' goes in `foo.elc'.
To execute a file of Emacs Lisp code, use M-x load-file. This command reads a file name using the minibuffer and then executes the contents of that file as Lisp code. It is not necessary to visit the file first; in any case, this command reads the file as found on disk, not text in an Emacs buffer.
Once a file of Lisp code is installed in the Emacs Lisp library
directories, users can load it using M-x load-library. Programs
can load it by calling load, a more primitive function that is
similar but accepts some additional arguments.
M-x load-library differs from M-x load-file in that it searches a sequence of directories and tries three file names in each directory. Suppose your argument is lib; the three names are `lib.elc', `lib.el', and lastly just `lib'. If `lib.elc' exists, it is by convention the result of compiling `lib.el'; it is better to load the compiled file, since it will load and run faster.
If load-library finds that `lib.el' is newer than
`lib.elc' file, it issues a warning, because it's likely
that somebody made changes to the `.el' file and forgot to
recompile it. Nonetheless, it loads `lib.elc'. This is
because people often leave unfinished edits the source file, and don't
recompile it until they think it is ready to use.
Because the argument to load-library is usually not in itself
a valid file name, file name completion is not available. Indeed, when
using this command, you usually do not know exactly what file name
will be used.
The sequence of directories searched by M-x load-library is
specified by the variable load-path, a list of strings that are
directory names. The default value of the list contains the directories where
the Lisp code for Emacs itself is stored. If you have libraries of
your own, put them in a single directory and add that directory
to load-path. nil in this list stands for the current default
directory, but it is probably not a good idea to put nil in the
list. If you find yourself wishing that nil were in the list,
most likely what you really want to do is use M-x load-file
this once.
Often you do not have to give any command to load a library, because
the commands defined in the library are set up to autoload that
library. Trying to run any of those commands calls load to load
the library; this replaces the autoload definitions with the real ones
from the library.
By default, Emacs refuses to load compiled Lisp files which were
compiled with XEmacs, a modified versions of Emacs--they can cause
Emacs to crash. Set the variable load-dangerous-libraries to
t if you want to try loading them.
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Lisp programs intended to be run in Emacs should be edited in Emacs-Lisp mode; this happens automatically for file names ending in `.el'. By contrast, Lisp mode itself is used for editing Lisp programs intended for other Lisp systems. To switch to Emacs-Lisp mode explicitly, use the command M-x emacs-lisp-mode.
For testing of Lisp programs to run in Emacs, it is often useful to evaluate part of the program as it is found in the Emacs buffer. For example, after changing the text of a Lisp function definition, evaluating the definition installs the change for future calls to the function. Evaluation of Lisp expressions is also useful in any kind of editing, for invoking noninteractive functions (functions that are not commands).
Read a single Lisp expression in the minibuffer, evaluate it, and print
the value in the echo area (eval-expression).
Evaluate the Lisp expression before point, and print the value in the
echo area (eval-last-sexp).
Evaluate the defun containing or after point, and print the value in
the echo area (eval-defun).
Evaluate all the Lisp expressions in the region.
Evaluate all the Lisp expressions in the buffer.
M-: (eval-expression) is the most basic command for evaluating
a Lisp expression interactively. It reads the expression using the
minibuffer, so you can execute any expression on a buffer regardless of
what the buffer contains. When the expression is evaluated, the current
buffer is once again the buffer that was current when M-: was
typed.
In Emacs-Lisp mode, the key C-M-x is bound to the command
eval-defun, which parses the defun containing or following point
as a Lisp expression and evaluates it. The value is printed in the echo
area. This command is convenient for installing in the Lisp environment
changes that you have just made in the text of a function definition.
C-M-x treats defvar expressions specially. Normally,
evaluating a defvar expression does nothing if the variable it
defines already has a value. But C-M-x unconditionally resets the
variable to the initial value specified in the defvar expression.
defcustom expressions are treated similarly.
This special feature is convenient for debugging Lisp programs.
Typing C-M-x on a defface expression reinitializes
the face according to the defface specification.
The command C-x C-e (eval-last-sexp) evaluates the Lisp
expression preceding point in the buffer, and displays the value in the
echo area. It is available in all major modes, not just Emacs-Lisp
mode. It does not treat defvar specially.
When the result of an evaluation is an integer, you can type C-x C-e a second time to display the value of the integer result in additional formats (octal, hexadecimal, and character).
If C-x C-e, or M-: is given a numeric argument, it inserts the value into the current buffer at point, rather than displaying it in the echo area. The argument's value does not matter. C-M-x with a numeric argument instruments the function definition for Edebug (see Instrumenting for Edebug: (elisp)Instrumenting section `Instrumenting' in the Emacs Lisp Reference Manual).
The most general command for evaluating Lisp expressions from a buffer
is eval-region. M-x eval-region parses the text of the
region as one or more Lisp expressions, evaluating them one by one.
M-x eval-buffer is similar but evaluates the entire
buffer. This is a reasonable way to install the contents of a file of
Lisp code that you are ready to test. Later, as you find bugs and
change individual functions, use C-M-x on each function that you
change. This keeps the Lisp world in step with the source file.
The two customizable variables eval-expression-print-level and
eval-expression-print-length control the maximum depth and length
of lists to print in the result of the evaluation commands before
abbreviating them. eval-expression-debug-on-error controls
whether evaluation errors invoke the debugger when these commands are
used; its default is t.
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The buffer `*scratch*' which is selected when Emacs starts up is provided for evaluating Lisp expressions interactively inside Emacs.
The simplest way to use the `*scratch*' buffer is to insert Lisp expressions and type C-j after each expression. This command reads the Lisp expression before point, evaluates it, and inserts the value in printed representation before point. The result is a complete typescript of the expressions you have evaluated and their values.
The `*scratch*' buffer's major mode is Lisp Interaction mode, which is the same as Emacs-Lisp mode except for the binding of C-j.
The rationale for this feature is that Emacs must have a buffer when it starts up, but that buffer is not useful for editing files since a new buffer is made for every file that you visit. The Lisp interpreter typescript is the most useful thing I can think of for the initial buffer to do. Type M-x lisp-interaction-mode to put the current buffer in Lisp Interaction mode.
An alternative way of evaluating Emacs Lisp expressions interactively is to use Inferior Emacs-Lisp mode, which provides an interface rather like Shell mode (see section Shell Mode) for evaluating Emacs Lisp expressions. Type M-x ielm to create an `*ielm*' buffer which uses this mode. For more information see that command's documentation.
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Emacs has facilities for running programs in other Lisp systems. You can run a Lisp process as an inferior of Emacs, and pass expressions to it to be evaluated. You can also pass changed function definitions directly from the Emacs buffers in which you edit the Lisp programs to the inferior Lisp process.
To run an inferior Lisp process, type M-x run-lisp. This runs
the program named lisp, the same program you would run by typing
lisp as a shell command, with both input and output going through
an Emacs buffer named `*lisp*'. That is to say, any "terminal
output" from Lisp will go into the buffer, advancing point, and any
"terminal input" for Lisp comes from text in the buffer. (You can
change the name of the Lisp executable file by setting the variable
inferior-lisp-program.)
To give input to Lisp, go to the end of the buffer and type the input, terminated by RET. The `*lisp*' buffer is in Inferior Lisp mode, which combines the special characteristics of Lisp mode with most of the features of Shell mode (see section Shell Mode). The definition of RET to send a line to a subprocess is one of the features of Shell mode.
For the source files of programs to run in external Lisps, use Lisp mode. You can switch to this mode with M-x lisp-mode, and it is used automatically for files whose names end in `.l', `.lsp', or `.lisp'.
When you edit a function in a Lisp program you are running, the easiest
way to send the changed definition to the inferior Lisp process is the key
C-M-x. In Lisp mode, this runs the function lisp-eval-defun,
which finds the defun around or following point and sends it as input to
the Lisp process. (Emacs can send input to any inferior process regardless
of what buffer is current.)
Contrast the meanings of C-M-x in Lisp mode (for editing programs to be run in another Lisp system) and Emacs-Lisp mode (for editing Lisp programs to be run in Emacs; see see section Evaluating Emacs Lisp Expressions): in both modes it has the effect of installing the function definition that point is in, but the way of doing so is different according to where the relevant Lisp environment is found.
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