View variable value in memory during Xcode debugging?

Question

I am debugging my C project in Xcode. Basically, I have many nested arrays, whose values I wish to inspect. They are present in the console (not sure if it is the right name) in the form of starting memory address, like

a (0x0000000100300010)
|-- b (0x0000000100105750)
    |-- c (0x0000000100108250)

I find it very hard to inspect the values of, say, array c in lldb. I've tried the po command in lldb, but no luck. So my first question is how do people usually do this inspection? I believe it is a common thing to do while debugging.

Then I read somewhere that one can achieve this by inspecting the memory contents at, say, 0x0000000100108250, which I did (screenshot as below).

It appears to me that the memory content is displayed as binary. I understand that this is physically more realistic, but to my goal (inspecting variable values), this is quite counterintuitive. My second question: is there a way of inspecting these memory contents as natural decimal numbers? If not, what sequence should I following in reading these binary numbers (specifically, what is 01 00 00 00)?

Enrico Granata · Accepted Answer · 2015-10-29 19:19:28Z

1

Imagine being stopped here:

int foo(int* ptr) {
  return *ptr; // HERE
}

and you happen to know that ptr points to a 5 element int array

(lldb) memory read -t int -c 5 `ptr`

will produce the following output for you:

(int) 0x7fff5fbff920 = 1
(int) 0x7fff5fbff924 = 2
(int) 0x7fff5fbff928 = 3
(int) 0x7fff5fbff92c = 4
(int) 0x7fff5fbff930 = 5

"memory read" should be obvious

-t int means "print elements of type int"

-c 5 means "print 5 elements"

`ptr` means "evaluate the string ptr as an expression and replace the result in the command" - this is a general LLDB trick where backticks introduce inline expressions in commands

answered Oct 29, 2015 at 19:19

Enrico Granata

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