Watch content of stl vector via gdb

Question

Hi there!

I've got a stl vector of custom class objects defined in a global namespace (yeah, evil, I know). Now I would like to set a watchpoint in gdb to monitor possible changes in a (public) member variable for a certain element of this vector. Something like:

watch custom_namespace::vec[123].aVariable

If I do this, then gdb (Version 7.1 on Ubuntu Lucid) segfaults. Are there alternative ways. Is this possible at all?

Answer 1

See if this applies to your case (from gdb manual):

Sometimes, gdb cannot set a hardware watchpoint because the data type of the watched expression is wider than what a hardware watchpoint on the target machine can handle. For example, some systems can only watch regions that are up to 4 bytes wide; on such systems you cannot set hardware watchpoints for an expression that yields a double-precision floating-point number (which is typically 8 bytes wide). As a work-around, it might be possible to break the large region into a series of smaller ones and watch them with separate watchpoints.

Try casting the address to (int*). Does it still segfault?

Also STL vector will move its content if it needs to extend the internal buffer, so your object might just be "stolen" from under the watchpoint.