为什么不能使用< NSDate进行比较？或者>？ [英] Why can't NSDate be compared using < or >?

问题描述

NSDate *date = [NSDate date];
NSDateFormatter *dateFormat = [[NSDateFormatter alloc]init];
[dateFormat setDateFormat:@"MM/dd/yyyy"];
NSLog([@"today is " stringByAppendingString:[dateFormat stringFromDate:date]]);
NSLog([@"firstBirthdayDate is " stringByAppendingString:[dateFormat stringFromDate:firstBirthdayDate]]);
NSLog([@"secondBirthdayDate is " stringByAppendingString:[dateFormat stringFromDate:secondBirthdayDate]]);
if ([firstBirthdayDate isEqualToDate:secondBirthdayDate])
    NSLog(@"First date is the same as second date");
if (firstBirthdayDate < date)
    NSLog(@"First date is earlier than today");
else
    NSLog(@"First date is later than today");

if (secondBirthdayDate < date)
    NSLog(@"Second date is earlier than today");

• 今天是11/08/2012


• firstBirthdayDate 是01/23/2012


• secondBirthdayDate 是01/23/2012


• Today is 11/08/2012
• firstBirthdayDate is 01/23/2012
• secondBirthdayDate is 01/23/2012

以下是我在日志中得到的信息：

Here's what I get in the log:




第一个日期与第二个日期相同

First date is the same as second date

第一个日期晚于今天

第二个日期早于今天

我想我会发疯...

推荐答案

使用 if（[date1 isEqualToDate：date2]）比较两个日期，否则你可以使用以下，

Use if ([date1 isEqualToDate:date2]) for comparing two dates or else you can use the following,

if ([date1 compare:date2] == NSOrderedSame)

if ([date1 compare:date2] == NSOrderedAscending)

if ([date1 compare:date2] == NSOrderedDescending)

> ，< 或 = 仅用于比较非指针。基本上我的理解是，当您使用这些运算符时，它可能是比较内存地址而不是内存中的值。所以你会得到意想不到的结果。

>, < or = are only for comparing non-pointers. Basically my understanding is that when you are using these operators, it might be comparing the memory addresses rather than the values in it. So you will get unexpected results.

从逻辑上讲，这是它的工作原理：

Logically, this is how it works:

    if (obj1 > obj2) {
        return NSOrderedDescending;
    }

    if (obj1 < obj2) {
        return NSOrderedAscending;
    }

    if (obj1 == obj2) {
        return NSOrderedSame;
    }

您可以使用任何比较语句来比较日期。

You can use any of the compare statements to compare dates.

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