问题
I'm using Xcode's debugger. While stopped at a breakpoint, is there a command I can type in the GDB command prompt to create a local variable? If so, how? Please provide an example.
I know I can do it in the code and then recompile the program, but I'm looking for a faster way.
回答1:
It's mentioned in the comments, but not as an answer: if you don't need to reference the variable in your code but just want to do some ad-hoc investigation, you can use Convenience Variables Start your variable with a $:
(gdb) set $foo = method_that_makes_something()
(gdb) set $bar = 15
(gdb) p $bar
$4 = 15
You'll notice when you print things it's prefixed with a numeric variable - you can use these to refer to that value later as well:
(gdb) p $4
$5 = 15
To reiterate: this doesn't actually affect the program's stack or anything, as that would break a lot of things, but it's useful if you just need a local playground, some loop variables, etc.
回答2:
Since a local variable would require stack space and the (compiled) code is tied to the stack layout, no you can't.
Comparing this with scripting languages is not quite appropriate.
回答3:
Values printed by the print command are saved in the GDB "value history". This allows you to refer to them in other expressions.
For example, suppose you have just printed a pointer to a structure and want to see the contents of the structure. It suffices to type
p *$
来源：https://stackoverflow.com/questions/8275135/gdb-create-local-variable