On Apr 27, 2009, at 08:10, Martijn van Exel wrote:
currentNode.lat = (double)[attributeDict
objectForKey:key];
...
Member 'lat' is a double. The above does not work. 'Pointer value
used where
float was expected'. So I should dereference?
currentNode.lat = (double *)[attributeDict
objectForKey:key];
"Dereference" is the wrong word. What you actually did was *cast*, but
that was the wrong thing to do anyway.
The result of [attributeDict objectForKey:key] is always an object
pointer (id, NSString*, NSNumber*, etc), never a scalar (int, double,
etc). There are three possibilities here:
1. It's a NSNumber object, in which case you'd use:
currentNode.lat = [[attributeDict objectForKey:key] doubleValue];
2. It's a NSString object, and you're certain that it contains a well-
formatted numeric representation, in which case you'd use NSString's
convenience method:
currentNode.lat = [[attributeDict objectForKey:key] doubleValue];
3. It's a NSString object, and you're *not* certain that it contains a
well-formatted numeric representation, in which case you can use
NSScanner's scanDouble: on the string to retrieve the number and then
check that there are no characters left over.
Of course, if the object is none of the above, we can't tell you how
to get a double out of it.
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