Why the block of iOS is decorated with copy

Before you read through the article, you may need to understand the basics of memory allocation.

By default, the Blockis archived on the stack and may be recycled at any time, and can be kept in a heap by copy, which is equivalent to being strongly referenced, so if you use self in the block, you need to weaken it by __weak or __unsafe_  unretained. Here is the sample code and its description, and the reader can try to print out the block memory in different situations

when the function's internal code ends, all variables stored in the stack in the function are released by the system, so if the property's block is assign decorated, wild pointer access occurs when it is accessed again.

[OBJC]  View plain  copy #import   "ViewController.h"       @interface  viewcontroller   ()    @property   (nonatomic, copy)  void (^myblock) ();      @end       @implementation  ViewController     -  (void) viewdidload  {       [super viewDidLoad];              //1 __NSGlobalBlock__   global block    stored in code area (storage method or function)         void (^MYBLOCK1) ()  = ^ ()  {            nslog (@ "I'm the Boss");       };       nslog (@ "%@", MyBlock1);                      //2 __NSStackBlock__   Stack block   stored in stack area      &NBSp; //block internal Access external variables        //block's essence is a structural body         int n = 5;       void (^myblock2) ()  = ^ ()  {            nslog (@ "I'm dick%d",  n);        };       nslog (@ "%@",  myblock2);                       //3 __NSMallocBlock__   Heap block  stored in heap area    do a copy operation on stack block        void (^MYBLOCK3) ()  =  ^ ()  {           nslog (@ "I'm dick%d",  n);        };       nslog (@ "%@",  [myblock3 copy]);                              /*        The above three examples show that blocks are stored in the code area when they do not have access to external variables,         when block access to external variables is stored in the stack area,  and at this point the scope will be released          The following example:       */       [self test];// When this code ends, all variables stored in the stack area in the test function are released by the system,  so if the property's block is assign decorated    a wild pointer access occurs when you access .        self.myblock ();        }     -  (void) test {        int n = 5;       [self setMyblock:^{            nslog (@ "%d", N);       }]; &nbs