Objective-C, retaining a variable after NSLog-output - objective-c

Question

I would like to know how weak property work in Objective-C.
In this example the value of the weak property "myString" in "myClass" is kept only when I print it with NSLog. Why is that?
#import <Foundation/Foundation.h>
#include <stdio.h>
#interface myClass : NSObject
#property (nonatomic, weak)NSString *myString;
- (void)readString;
#end
#implementation myClass
#synthesize myString;
- (void)readString
{
const int MAXBUFFER = 80;
char buffer[MAXBUFFER+1];
NSLog(#"Input string:");
fgets(buffer, MAXBUFFER, stdin);
NSString *tempString = [[NSString alloc] initWithUTF8String:buffer];
myString = tempString;
NSLog(#"myString: %#", myString); // Why does this line make all the difference?
}
#end
int main(int argc, const char * argv[])
{
#autoreleasepool
{
myClass *myInstance = [[myClass alloc] init];
[myInstance readString];
NSLog(#"myInstance.myString: %#", myInstance.myString);
}
return 0;
}
If the NSLog-line in the readString-method is commented out myInstance.myString becomes "(null)". Why??

Answer 1

From Apple:
weak Specifies that there is a weak (non-owning) relationship to the
destination object. If the destination object is deallocated, the
property value is automatically set to nil.
So Basically when arc insert code into [readString], he does:
NSString *tempString = [[NSString alloc] initWithUTF8String:buffer];
myString = tempString;
// + arc [tempString release]
So your tempString no longer exist outside the method, because nothing retain it.
But when you add NSlog inside [readString] with myString, NSLog will keep reference to the pointer (i don't know exactly how), but he actually does since he logs them.