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(emacs)Debugger Operation

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Debugger Operation
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   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.  The
debugger displays the source files of the program by visiting them in
Emacs buffers.  An arrow (`=>') in one of these buffers indicates the
current execution line.(1)  Moving point in this buffer does not move
the arrow.

   You can start editing these source files at any time in the buffers
that display them.  The arrow is not part of the file's text; it
appears only on the screen.  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.

   If you wish, you can control your debugger process entirely through
the debugger buffer, which uses a variant of Shell mode.  All the usual
commands for your debugger are available, and you can use the Shell mode
history commands to repeat them.  Note: Shell Mode.

   ---------- Footnotes ----------

   (1) Under a window system the arrow is displayed in the marginal
area of the Emacs window.