Hi,
I have just spent time investigating why
an if statement involving an [array count] was apparently misbehaving.
The construct was this:
if(3 < ([zAry count] - 10))
It delivers a (to me unexpected) result when [zAry count] < 10.
In fact
if(3 >= ([zAry count] - 10))
also returns an unexpected result for the same [zAry count] value.
The reason is that [zAry count] returns a result of type NSUInteger!!!!
Thus for this type of comparison I need to coerce the type to NSInteger i.e.
if(3 < ((NSInteger)[zAry count] - 10))
Why might the Cocoa developers have chosen to do this?
Julius
======
Here to satisfy possible curiosity is my test code snippet and results
NSMutableArray * zAry = [[NSMutableArray alloc]init];
for(NSInteger i = 0; i < 7; i++) {
[zAry addObject:@"obj"];
}
NSLog(@"[zAry count] = %d",[zAry count]);
if(3 < ([zAry count] - 9)) {
NSLog(@"A1: wrong result for: 3 < %d",([zAry count] - 9));
} else {
NSLog(@"A2: correct result for: 3 < %d",([zAry count] - 9));
}
if(3 >= ([zAry count] - 9)) {
NSLog(@"B1: correct result for: 3 >= %d",([zAry count] - 9));
} else {
NSLog(@"B2: wrong result for: 3 >= %d",([zAry count] - 9));
}
NSInteger zAryCount = [zAry count];
if(3 < (zAryCount - 10)) {
NSLog(@"C1: wrong result for: 3 < %d",(zAryCount - 9));
} else {
NSLog(@"C2: correct result for: 3 < %d",(zAryCount - 9));
}
NSUInteger zUInt = 7;
if (3 < (zUInt - 9)) {
NSLog(@"E1: wrong result for: 3 < %d",(zUInt - 9));
} else {
NSLog(@"E2: correct result for: 3 < %d",(zUInt - 9));
}
// these produce the required result
if(3 < ((NSInteger)[zAry count] - 9)) {
NSLog(@"F1: wrong result for: 3 < %d",([zAry count] - 9));
} else {
NSLog(@"F2: correct result for: 3 < %d",([zAry count] - 9));
}
if(3 >= ((NSInteger)[zAry count] - 9)) {
NSLog(@"G1: correct result for: 3 >= %d",([zAry count] - 9));
} else {
NSLog(@"G2: wrong result for: 3 >= %d",([zAry count] - 9));
}
2011-05-29 20:41:19.107 TestIf[4858:903] [zAry count] = 7
2011-05-29 20:41:19.110 TestIf[4858:903] A1: wrong result for: 3 < -2
2011-05-29 20:41:19.110 TestIf[4858:903] B2: wrong result for: 3 >= -2
2011-05-29 20:41:19.111 TestIf[4858:903] C2: correct result for: 3 < -2
2011-05-29 20:41:19.111 TestIf[4858:903] E1: wrong result for: 3 < -2
2011-05-29 20:41:19.111 TestIf[4858:903] F2: correct result for: 3 < -2
2011-05-29 20:41:19.112 TestIf[4858:903] G1: correct result for: 3 >= -2
http://juliuspaintings.co.uk
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