blocks|key|372880|text|如果这是为了显示目的，请查看NSNumberFormatter。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|372881|如果由于某些原因，您确实想在计算中舍入双精度数，则可以使用标准的C+round()函数。|style|CODE|372882|entityMap|0|LINK|mutability|MUTABLE|url|http://developer.apple.com/documentation/Cocoa/Reference/Foundation/Classes/NSNumberFormatter_Class/Reference/Reference.html^0|E|H|0|0|Y|7|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@$A|Q|B|R|1|S]]|C|$]]|$1|D|3|E|5|6|7|T|8|@$A|U|B|V|F|G]]|9|@]|C|$]]|$1|H|3|-4|5|6|7|W|8|@]|9|@]|C|$]]]|I|$J|$5|K|L|M|C|$N|O]]]]

If this is for display purposes, take a look at <a href="http://developer.apple.com/documentation/Cocoa/Reference/Foundation/Classes/NSNumberFormatter_Class/Reference/Reference.html" rel="nofollow noreferrer">NSNumberFormatter</a>.

If you really want to round the double in your calculations for some reason, you can use the standard C <code>round()</code> function.

blocks|key|372900|text|使用NSDecimalRound()可以将NSDecimal四舍五入为指定的位数。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|372901|double+d+=+[[NSDate+date]+timeIntervalSince1970];
NSDecimal+in+=+[[NSNumber+numberWithDouble:d]+decimalValue];
NSDecimal+out;
NSDecimalRound(+&out,+&in,+2,+NSRoundUp+);

NSDecimalNumber+*result+=+[NSDecimalNumber+decimalNumberWithDecimal:out];|code-block|syntax|javascript|372902|entityMap|0|LINK|mutability|MUTABLE|url|http://developer.apple.com/library/ios/#documentation/Cocoa/Reference/Foundation/Miscellaneous/Foundation_Functions/Reference/reference.html#//apple_ref/c/func/NSDecimalRound^0|2|G|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

A NSDecimal can be rounded to a specified number of digits with <a href="http://developer.apple.com/library/ios/#documentation/Cocoa/Reference/Foundation/Miscellaneous/Foundation_Functions/Reference/reference.html#//apple_ref/c/func/NSDecimalRound" rel="nofollow">NSDecimalRound()</a>.

<pre><code>double d = [[NSDate date] timeIntervalSince1970];
NSDecimal in = [[NSNumber numberWithDouble:d] decimalValue];
NSDecimal out;
NSDecimalRound( &amp;out, &amp;in, 2, NSRoundUp );

NSDecimalNumber *result = [NSDecimalNumber decimalNumberWithDecimal:out];
</code></pre>

blocks|key|3590845|text|如果你真的想要点后剩下的两位数，乘以100，使用round()函数对其进行舍入，再将其除以100。然而，这并不能保证它在点之后只有两位数，因为通过再次除以它，你可能得到一个不能真正用浮点符号表示的数字，而当你期望0.1时，你实际上可能得到0.09999...，这是因为你不能真正使用浮点符号来表达0.1。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3590846|如果您只想将其四舍五入为点后的两位数，则可以按照建议使用NSNumberFormatter或直接使用：|3590847|printf("%25.2f\n",+yourTimeInterval);
NSLog(@"%25.2f\n",+yourTimeInterval);|code-block|syntax|javascript|3590848|或者，要获取NSString，您还可以使用以下命令，这可能比使用NumberFormatter更快(但是，它不会根据用户偏好进行本地化)：|3590849|NSString+*+intervalStr+=+nil;
char+*+intervalStrTmp+=+NULL;
asprintf(&intervalStrTmp,+"%25.2f",+yourTimeInteval);
if+(intervalStrTmp)+{
++intervalStr+=+[[NSString+alloc]+initWithUTF8String:intervalStrTmp];
++free(intervalStrTmp);
}|3590850|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

If you really want two digits left after the dot, multiply by 100, round it using round() function, divide it by 100 again. However, this will not guarantee that it really has only two digits after the dot, since by dividing it again, you may get a number that cannot really be expressed with floating point notation and when you expect 0.1 you may in fact get 0.09999..., that's because you cannot really express 0.1 using floating point notation.

If you just want to round it to two digits after the dot for display purposes, you can use NSNumberFormatter as has been suggested or just use:

<pre><code>printf("%.2f\n", yourTimeInterval);
NSLog(@"%.2f\n", yourTimeInterval);
</code></pre>

or to get an NSString, you can also use the following, which is probably even faster than using a NumberFormatter (however, it won't be localized according to the user prefs):

<pre><code>NSString * intervalStr = nil;
char * intervalStrTmp = NULL;
asprintf(&amp;intervalStrTmp, "%.2f", yourTimeInteval);
if (intervalStrTmp) {
 intervalStr = [[NSString alloc] initWithUTF8String:intervalStrTmp];
 free(intervalStrTmp);
}
</code></pre>

blocks|key|372831|text|这个HumanReadableTimeInterval有帮助吗？不过，它会返回一个NSString。或者，您可以通过乘以100来舍入自己，转换为整数，然后再次除以100。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|372832|entityMap|0|LINK|mutability|MUTABLE|url|http://www.cocoadev.com/index.pl?HumanReadableTimeInterval^0|2|P|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

Does this <a href="http://www.cocoadev.com/index.pl?HumanReadableTimeInterval" rel="nofollow noreferrer">HumanReadableTimeInterval</a> help? It returns a NSString, though.
Alternatively, you can round yourself by multiplying with 100, converting to an integer and dividing through 100 again.

blocks|key|4437558|text|在绝大多数情况下，只应在显示时对数字进行四舍五入。浮点数的属性(双精度或非双精度)使得不可能以固定精度存储某些数字。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4437559|有关设置数字格式以使其显示为两位小数的信息，请参阅see+this+other+post。|offset|length|4437560|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/560517/how-to-set-the-float-value-to-two-decimal-number-in-objective-c/560525#560525^0|0|P|J|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@]|9|@$D|P|E|Q|1|R]]|A|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|M]]]]

In the vast majority of cases rounding a number is something you should only do at display time. The properties of floating-point numbers (double or not) make it impossible to store certain numbers at a fixed-precision.

For information about formatting a number so it displays to two decimal places, <a href="https://stackoverflow.com/questions/560517/how-to-set-the-float-value-to-two-decimal-number-in-objective-c/560525#560525">see this other post</a>.

blocks|key|3590824|text|我只会使用ANSI的round()函数。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3590825|entityMap^0|A|7|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

I would just use the ANSI C <code>round()</code> function.

blocks|key|3590877|text|您可以始终使用以下命令对数字进行舍入：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3590878|double+round2dec(double+a)+{+return+round(a+*+100)+/+100;+}|code-block|syntax|javascript|3590879|但可能的情况是，将结果表示为双精度型时，不会只有两个小数。|3590880|现在，如果使用==符号，您的意思是两个双精度数之间的比较仅限于第二个小数。以下是您可以执行的操作：|3590881|fabs(round2dec(NSTimeInterval)+-+round2dec(double))+<+std::numeric_limits<double>::epsilon()|3590882|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|D|7|S|8|@]|9|@]|A|$E|F]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

You can always round the number using:

<pre><code>double round2dec(double a) { return round(a * 100) / 100; }
</code></pre>

But chances are that the representation of the result as a double will not have only 2 decimals. 

Now, if by using the == sign, you meant that the comparison of your two double numbers is made only to the second decimal. Here is what you can do:

<pre><code>fabs(round2dec(NSTimeInterval) - round2dec(double)) &lt; std::numeric_limits&lt;double&gt;::epsilon()
</code></pre>

NSTimeInterval == double; (e.g. 169.12345666663)

How can I round up this double so that there are only 2 digits left after the "dot"? 
It would be very good if the result is a NSNumber.

NSTimeInterval to readable NSNumber

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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NSTimeInterval == double；(例如169.12345666663)如何四舍五入这个双精度数，使“点”后只剩下两位数？如果结果是NSNumber，那就太好了。

问可读NSNumber的NSTimeInterval
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