gdb.info: Breakpoints

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Breakpoints, watchpoints, and catchpoints

A "breakpoint" makes your program stop whenever a certain point in the
program is reached.  For each breakpoint, you can add conditions to
control in finer detail whether your program stops.  You can set
breakpoints with the `break' command and its variants (*note Setting
breakpoints: Set Breaks.), to specify the place where your program
should stop by line number, function name or exact address in the
program.
   In HP-UX, SunOS 4.x, SVR4, and Alpha OSF/1 configurations, you can
set breakpoints in shared libraries before the executable is run.
There is a minor limitation on HP-UX systems: you must wait until the
executable is run in order to set breakpoints in shared library
routines that are not called directly by the program (for example,
routines that are arguments in a `pthread_create' call).
   A "watchpoint" is a special breakpoint that stops your program when
the value of an expression changes.  You must use a different command
to set watchpoints (*note Setting watchpoints: Set Watchpoints.), but
aside from that, you can manage a watchpoint like any other breakpoint:
you enable, disable, and delete both breakpoints and watchpoints using
the same commands.
   You can arrange to have values from your program displayed
automatically whenever GDB stops at a breakpoint.  *Note Automatic
display: Auto Display.
   A "catchpoint" is another special breakpoint that stops your program
when a certain kind of event occurs, such as the throwing of a C++
exception or the loading of a library.  As with watchpoints, you use a
different command to set a catchpoint (*note Setting catchpoints: Set
Catchpoints.), but aside from that, you can manage a catchpoint like any
other breakpoint.  (To stop when your program receives a signal, use the
`handle' command; see *Note Signals: Signals.)
   GDB assigns a number to each breakpoint, watchpoint, or catchpoint
when you create it; these numbers are successive integers starting with
one.  In many of the commands for controlling various features of
breakpoints you use the breakpoint number to say which breakpoint you
want to change.  Each breakpoint may be "enabled" or "disabled"; if
disabled, it has no effect on your program until you enable it again.
   Some GDB commands accept a range of breakpoints on which to operate.
A breakpoint range is either a single breakpoint number, like `5', or
two such numbers, in increasing order, separated by a hyphen, like
`5-7'.  When a breakpoint range is given to a command, all breakpoint
in that range are operated on.