I'm having trouble viewing the contents of that specific variable, it appears that it is out of context for the debugger.
Ignoring the Xcode GUI and only using the GDB console I have added a breakpoint at "Packet >> mess;" and used the command "up" to set the current context to "#6 0x000add0e in sf::Packet::operator>> ()", and from there I should be able to "print Length", but it says "No symbol "Length" in current context.".
And in the GUI that particular method (and all above it) (talking about #6 0x000add0e in sf::Packet::operator>>), when I have selected it, I can't view Local variables, only "Globals" and "Registers". Any ideas?