On May 26, 2009, at 8:33 AM, vinai wrote:
I think I am missing something really basic here with NSString.
Actually, it seems you're missing stuff much more basic than that.
You seem to not understand the difference between a pointer and an
object (which a pointer might point to).
if ([oPanel runModalForDirectory:nil file:nil types:nil] ==
NSOKButton)
{
NSArray * files = [oPanel filenames];
/* Process files */
for( i = 0; i < [files count]; i++ )
{
[rawFileName initWithString: [[files objectAtIndex:i]
stringByStandardizingPath]];
This is very atypical. You should not be init-ing an object except
immediately upon allocating it. Typically, this is done in an
expression which combines the +alloc message with a -init... message.
So, for example:
rawFileName = [[NSString alloc] initWithString: [[files
objectAtIndex:i] stringByStandardizingPath]];
That bring us to issues of memory management, for which you should
read the memory management guide. In this case, you would have to
make sure you release the object pointed to by rawFileName when you're
done with it.
However, why are you attempting to init another object, at all? The
expression [[files objectAtIndex:i] stringByStandardizingPath] returns
a pointer to a string object, already. There's a pretty good chance
that you can just make use of that string object directly. If you
need to keep it around, you could retain it and then release it later.
NSLog(@"Logging the file name variable");
NSLog(rawFileName);
NSLog(@"Logging the called file path object directly");
NSLog([[files objectAtIndex:i] stringByStandardizingPath]);
}
}
and this is the output from that section of code:
2009-05-26 09:18:41.931 REMI[19710:807] Logging the file name variable
2009-05-26 09:18:41.932 REMI[19710:807] Logging the called file path
object directly
2009-05-26 09:18:41.932 REMI[19710:807] /Users/vinai/Desktop/
rawTestData/P04608.7
rawFileName is declared to be an NSString * in my object's header
file.
And here is why I think you misunderstand the difference between a
pointer and an object which it might point to.
Having declared a pointer as an instance variable means that each of
your objects has a pointer. It does not mean that each of your
objects has a string object. Unless you explicitly assign that
pointer to point to something, it points to nothing.
So why does printing out the string returned by the
stringByStandardizingPath function work okay, but not when
initializing an NSString * variable with it ?
You did not initialize the rawFileName variable with the above code.
You attempted to initialize the object to which rawFileName pointed.
There are two problems: 1) rawFileName points to nothing, and 2) if it
did point to something, that object should have already been
initialized and you're not allowed to initialize it again.
You can choose a couple of alternative approaches:
*) You could change what rawFileName points to by assigning it the
address of a different object. If you do that, be sure to get memory
management right.
*) You could have rawFileName point to a mutable string object, and
change the content of that string object. That's different from
attempting to reinitialize the object.
Regards,
Ken
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