Xcode – How to change variables value while debugging with LLDB in Xcode

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In Xcode, GDB allows you to change local variables while debugging (see how to change NSString value while debugging in XCode?). Does LLDB offer a similar functionality? If so, how can we use it?

Best Answer

expr myString = @"Foo"

(lldb) help expr
Evaluate a C/ObjC/C++ expression in the current program context, using variables currently in scope. This command takes 'raw' input (no need to quote stuff).

Syntax: expression --

Command Options Usage: expression [-f ] [-G ] [-d ] [-u ] -- expression [-o] [-d ] [-u ] -- expression 

   -G <gdb-format>  ( --gdb-format <gdb-format> )
        Specify a format using a GDB format specifier string.

   -d <boolean>  ( --dynamic-value <boolean> )
        Upcast the value resulting from the expression to its dynamic type
        if available.

   -f <format>  ( --format <format> )
        Specify a format to be used for display.

   -o  ( --object-description )
        Print the object description of the value resulting from the
        expression.

   -u <boolean>  ( --unwind-on-error <boolean> )
        Clean up program state if the expression causes a crash, breakpoint
        hit or signal.

Examples:

expr my_struct->a = my_array[3]
expr -f bin -- (index * 8) + 5
expr char c[] = "foo"; c[0]

IMPORTANT NOTE: Because this command takes 'raw' input, if you use any command options you must use ' -- ' between the end of the command options and the beginning of the raw input.

'expr' is an abbreviation for 'expression'

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