Sometimes you want to a breakpoint to happen only when certain conditions are true. Such as a session having started, a file or socket being open or an iteration being at a certain point. Conditional breakpoints can help with this.
Regexp, temporary and normal breakpoints can all be made conditional by adding the suffix:
if [CONDITION]
Here [CONDITION] is a boolean expression, which, in GDB is true if the result is nonzero, otherwise it is false. The condition can include a function call, the value of a variable or the result of any GDB expression.
A common use case is using a conditional breakpoint to pause execution of your program on the [N]th iteration of a loop by typing something like:
break foo if i == [N]
For example:
break foo if i == 4
You can also make an existing breakpoint conditional by using the condition command. If you have an existing breakpoint (say 2) then you can add a condition to it with:
condition 2 i == 4
Type help condition at the GDB prompt for more.