setting a breakpoint in a specific line inside a function with 'gdb'

Question

I am trying to set a breakpoint to the fifth line inside a member function of a class(a class that I created) with 'gdb'.

From here I understood just how to set a breakpoint at the begining of the the function,but I want to set it on a specific line inside the function, or a specific offset from the begining of this function.

In general is there a way in 'gdb' to set a breakpoint to a line by setting an offset from another breakpoint I already have ?

Thanks !

Answer 1

You can create a breakpoint at an offset from the current stopped position with gdb breakpoint +<offset>.

You can also create a breakpoint on a specific line number using either gdb break <linenumber> (for the current source file) or gdb break <filename>:<linenumber> (for a file other than the current file).

More details in the docs.

Answer 2

There isn't a way to set a breakpoint relative to the start of a function such that it will retain its relative position if the source file is modified. This would sometimes be useful; but it is just a feature that nobody has added to gdb.

It could maybe be emulated from Python, though it couldn't work exactly the way that ordinary breakpoints work, because Python doesn't have access to the breakpoint resetting mechanism inside gdb.

A one-shot solution can be done either as shown in the other answer or from Python.

When I have needed this sort of functionality -- a breakpoint mid-function that is reasonably robust against source changes -- I have used "SDT" static probe points. These let you name such spots in your source.