Filter
Top Products
say, to just set a watchpoint on a variable name, and specify a condition that tests
whether the new value is an interesting one.
Break conditions can have side effects, and may even call functions in your program.
This can be useful, for example, to activate functions that log program progress, or to
use your own print functions to format special data structures. The effects are completely
predictable unless there is another enabled breakpoint at the same address. (In that
case, GDB might see the other breakpoint first and stop your program without checking
the condition of this one.) Note that breakpoint commands are usually more convenient
and flexible than break conditions for the purpose of performing side effects when a
breakpoint is reached (see “Breakpoint command lists” (page 61)).
Break conditions can be specified when a breakpoint is set, by using 'if' in the arguments
to the break command. See “Setting breakpoints” (page 52). They can also be changed
at any time with the condition command.
You can also use the if keyword with the watch command. The catch command does
not recognize the if keyword; condition is the only way to impose a further condition
on a catchpoint.
condition bnum expression Specify expression as the break condition for
breakpoint, watchpoint, or catchpoint number
bnum. After you set a condition, breakpoint bnum
stops your program only if the value of
expression is true (nonzero, in C). When you
use condition, GDB checks expression
immediately for syntactic correctness, and to
determine whether symbols in it have referents
in the context of your breakpoint. If expression
uses symbols not referenced in the context of the
breakpoint, GDB prints an error message:
No symbol "foo" in current context.
GDB does not actually evaluate expression at the
time the condition command (or a command
that sets a breakpoint with a condition, like break
if ...) is given, however. See “Expressions”
(page 83).
condition bnum
Remove the condition from breakpoint number
bnum. It becomes an ordinary unconditional
breakpoint.
A special case of a breakpoint condition is to stop only when the breakpoint has been
reached a certain number of times. This is so useful that there is a special way to do it,
using the ignore count of the breakpoint. Every breakpoint has an ignore count,
which is an integer. Most of the time, the ignore count is zero, and therefore has no
effect. But if your program reaches a breakpoint whose ignore count is positive, then
60 Stopping and Continuing