New tricks that I have learned in using debuggers

May 24, 2007 at 8:19 pm (C/C++)

In gdb/dbx, we can see the variable using addresses. Suppose a structure [struct Box * b] is not deallocated but we are setting it to NULL i.e. b = NULL. We can not access that structure using b. But if we know the address pointed by b [we can get it using print b], we can access it like *(struct Box *) (0x4f2b2448) [assuming 0x4f2b2448 is the address that b points]. Obviously this is a very simple thing. But, I have used it for the first time. Similarly, when setting watchpoints over variables like watch b->length, if the control goes to some other place where this variable b is not in scope, that watchpoint will be deleted. [Atleast this happens in old gdb versions, I’m using SuSE 8]. So, in those cases you can put watch point over address so that it is accessible from anywhere. watch ((struct Box *)(0x4f2b2448))->length works fine.