Often times we would want to hold some temporary variables when debugging with
lldb. We can make use of
expression in such cases. An
expression, short form
e or
expr evaluates the given statement. If we use an assignment with a variable starting with
$, that variable will be available through out and can be used in other expressions.
(lldb) expr NSRange $range1 = NSMakeRange(0, 3);
(lldb) expr [@"Hi Olive" substringWithRange:(NSRange)$range1];
(NSTaggedPointerString *) $9 = 0x7a858d27bb2607ed @"Hi "
Since we are in single-line expression mode, there are slight differences in the way the expressions work. We need to cast
NSRange. A better option in this case is to use the multi-line expression mode. For that, first enter
expr↩ followed by a carriage return. The lldb is now in multi-line expression mode where we can enter normal Objective-C (or Swift) code with each line terminated with a semi-colon and an empty line after the final statement will evalute all the expressions and exit the mode.
(lldb) expr
Enter expressions, then terminate with an empty line to evaluate:
1 NSRange range = NSMakeRange(9, 4);
2 NSString *str = @"Slice of Life";
3 [str substringWithRange:range];
4
(NSTaggedPointerString *) $4 = 0x7a858d42fd26039d @"Life"
(lldb)
Multi-line expression with
lldb makes debugging much better.