On Jul 22, 2008, at 8:33 PM, Jeff Brown wrote:
What do I need to do in the following code to get theString to take
the value I'm giving it in foo i.e. "Hi there"?
- (void) aMethod
{
NSString* theString = @"";
[self foo:theString];
}
- (NSString*) foo:(NSString*)aString
{
NSString* stringB = @"Hi there";
aString = stringB;
}
If you're just inquiring about how to use the language, I think you're
looking for:
- (void) aMethod
{
NSString* theString = nil; // No sense initializing it with a pointer
to a string, when you're about to reassign it.
[self foo:&theString]; // Don't pass the pointer theString, pass the
pointer to the pointer theString so that -foo: can write through the
pointer-to-pointer to modify the pointer. Makes sense? ;)
}
- (void) foo:(NSString**)aString // Note the extra asterisk, which
establishes an additional level of indirection
{
*aString = @"Hi there"; // Use the asterisk to dereference the
pointer-to-pointer to modify the pointed-to pointer
}
However, that's a pretty uncommon technique when using Cocoa. More
common would be for a method to return a string.
Also, keep the memory management guidelines in mind. They are
obscured a bit in trivial examples like this, which only involve
string literals. The convention is that callers of the -foo: method,
since they are not invoking +alloc, +new, -copy..., or -mutableCopy...
need not concern themselves with releasing the returned object. So, -
foo: must be implemented to take care of that itself, often by making
sure the returned object has been autoreleased.
Lastly, the naming conventions for a method like -foo: would be to
prefix it with "get". Something like "getTitle:". Again, though,
more common would be just a "title" method which returned the title
rather than outputting it via a by-reference parameter.
Cheers,
Ken
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