iOS : NSInteger and NSUInteger comparison

问题

Surprise!

I've a variable like this,

NSInteger index = 0;

I'm comparing it with one of subviews count (which returns NSUInteger) like this,

if((index-1) <= [[currentmonth subviews] count]) 
{
    NSLog(@"true");
}
else
{
    NSLog(@"false");
}

This always giving false.

but If I'll do like this,

if ((index-1) <= 42) {
    NSLog(@"true");
} else {
    NSLog(@"false");
}

This always giving true.

I feel that, this because we can't compare NSInteger with NSUInteger correct?

I caught this issue, when I have a working solution based on this logic. But its not true at all.

回答1:

I've found this, NSUInteger vs NSInteger, int vs unsigned, and similar cases

This answer gives the good explanations on this!

---

You should also be aware of integer conversion rules when dealing with NSUInteger vs. NSInteger:

The following fragment for example returns 0 (false) although you'd expect it to print 1 (true):

NSInteger si = -1;
NSUInteger ui = 1;
printf("%d\n", si < ui);

The reason is that the [si] variable is being implicitly converted to an unsigned int!

See CERT's Secure Coding site for an in-depth discussion around these 'issues' and how to solve them.

来源：https://stackoverflow.com/questions/25480412/ios-nsinteger-and-nsuinteger-comparison