ios - How can I retain a local variable that is set in a block? -

so have:

@interface testappcontrol : nsobject {     nsstring *s; } 

and in block want do

[sendapi setgroupwithname:groupname completionhandler:^(nsarray *errors) {     s = @"something"; }];  nslog(@"%@", s); //<--- s null 

so want keep value "something" after leave block. possible arc?

declare __block variable, can use outside block , alter inside block.

__block nsstring *s = nil;  void(^block)(void) = ^ {     s = @"something"; }; block(); nslog(@"%@", s);  s = @"blah"; nslog(@"%@", s);  block(); nslog(@"%@", s);