Retain and release of Object-C (retention and release)

In object-C, the system automatically saves a reference counter for each created object. When an object is created, the reference count is set to 1. Each time the object must be kept, you need to send a (called) Retain to add 1 to the reference count. When you no longer need an object, you can send a release message to reduce the reference count by 1. When the reference count is 0, the system will release its memory (by sending the dealloc message to the object, that is, truly revoking the object's memory ). In addition, you can use retaincount to obtain the reference count of this object. The returned type is an nsuinteger. The basic call method is as follows:
[OBJ retain];
[OBJ release];
[OBJ retaincount];

1. ExampleCode:
// 1. classa. h
# Import <Foundation/nsobject. h>

@ Interface classa: nsobject

@ End

// 2. classa. m
# Import "classa. H"

@ Implementation classa

// Declaration in. H. You do not need to declare the dealloc method.
-(Void) dealloc {
Printf ("deallocing classa \ n ");
[Super dealloc];
}
@ End

// 3. Main. m
# Import <stdio. h>
# Import "classa. H"

Int main (INT argc, const char * argv []) {
Printf ("Test Case 1: \ n ");
Classa * a1 = [[classa alloc] init];
Classa * a2 = [[classa alloc] init];

Printf ("A1 retain count: % I \ n", [a1 retaincount]);
Printf ("A2 retain count: % I \ n", [A2 retaincount]);

Printf ("Test Case 2: \ n ");
[A1 retain]; // 2
[A1 retain]; // 3
[A2 retain]; // 2

Printf ("A1 retain count: % I \ n", [a1 retaincount]);
Printf ("A2 retain count: % I \ n", [A2 retaincount]);

Printf ("Test Case 3: \ n ");
[A1 release]; // 2
[A2 release]; // 1

Printf ("A1 retain count: % I \ n", [a1 retaincount]);
Printf ("A2 retain count: % I \ n", [A2 retaincount]);

// Release
[A1 release]; // 1 // note that there must be several release records.
[A1 release]; // 0 // and only call delloc once
[A2 release]; // 0

Return 0;
}

2. Compile and run:
Gcc-fconstant-string-class = nsconstantstring-C main. M-I/gnustep/system/library/Headers
Gcc-C classa. M-I/gnustep/system/library/Headers
GCC main. O classa. O-o main-L/gnustep/system/library/libraries/-lobjc-lgnustep-Base

$./Main.exe
Test Case 1:
A1 retain count: 1
A2 retain count: 1
Test Case 2:
A1 retain count: 3
A2 retain count: 2
Test Case 3:
A1 retain count: 2
A2 retain count: 1
Deallocing classa
Deallocing classa
 
3. Description:
(1). There are several restyles, there must be several release, and delloc will only be called once;
(2 ). one principle is that you have to release the memory you have applied for. Instead of applying for it, please do not release it at will. This is not your responsibility;
(3) Each time a retain object is retained, it should be release or autoreleas.