Question

Whilst debugging in Xcode_3.1.2 I am pretty sure I could see the contents of my NSString arrays. However after upgrading to 3.2 I only see the following …

I know I can print the object in (gdb) using “po planetArray” or simply click in the debugger and “print description to console” I am just curious, as I am sure it worked prior to upgrading. Anyone know anything about this?

cheers gary

edit: data formatters is on and it shows what you see above …

Answer 1

This is because GDB acts as if the variable you are viewing is out of scope while it really just is confused about what each part function or method call of the data formatter is returning (the data formatter is the “{(unichar *)Xcode_CFStringSummary($VAR, $ID)}:s” part you are seeing.
When you are debugging and you are in a method where you know a local variable must be in scope right now, open the debugger window and the area where you can see “Variable”, “Value” and “Summary” column titles double click the “Summary” row entry for the variable you are interested in and enter the following (for array types like NSArray or NSCFArray):

“{(int)[$VAR count]} objects {(NSString *)[(NSArray *)$VAR description]}:s”

then press return. You have now overwritten the default data formatter provided by Xcode’s GDB extension (to be found in various plists at “/Developer/Library/Xcode/CustomDataViews/”) with your own data formatter string.

Your own overrides are saved at “~/Library/Application Support/Developer/Shared/Xcode/CustomDataViews/CustomDataViews.plist” and if you want to have the Apple default data formatter back just double click the row for a variable of the same type and delete whatever is there.

The nitty-gritty details: In the custom expression above the “{}” construct tells GDB to execute a command (as if you where executing it from GDB’s debugger command line, which means the same restrictions apply: you need to specify the return type in cast parens in front of every function or method which returns something). The “:s” behind the closing curly brace tells Xcode and GDB to reference the “Summary” column. Also valid would be “:v” which references the “Value” column which most of the time is just the pointer value. Everything that is outside of the curly braces is shown verbatim.
Unfortuntely curly braces can’t be nested which invalidates ternary operator conditionals.

So with the above data formatter you should see the following for an empty NSArray:

“0 objects (\n)”

If you want to write your own data formatters as GDB extensions (equivalent to specifying a function akin to Xcode_CFStringSummary above) you can do so. Take a look at the following header: “/Developer/Applications/Xcode.app/Contents/PlugIns/GDBMIDebugging.xcplugin/Contents/Headers/DataFormatterPlugin.h”

it will tell you all you need to know. But it can be hard to get it right. It might be easier and less error prone to just define another method on your class and call that from the data formatter string instead of “description”.