blocks|key|1728407|text|您可以使用以下命令将NSString转换为double|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1728408|double+myDouble+=+[myString+doubleValue];|code-block|syntax|javascript|1728409|然后，四舍五入到最接近的整数可以如下所示|1728410|int+myInt+=+(int)(myDouble+%2B+(myDouble>0+?+0.5+:+-0.5))|1728411|老实说，我不确定有没有比这更简单的转换回字符串的方法|1728412|NSString*+myNewString+=+[NSString+stringWithFormat:@"%25d",+myInt];|1728413|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|U|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

You can convert an NSString into a double with 

<pre><code>double myDouble = [myString doubleValue];
</code></pre>

Rounding to the nearest int can then be done as

<pre><code>int myInt = (int)(myDouble + (myDouble&gt;0 ? 0.5 : -0.5))
</code></pre>

I'm honestly not sure if there's a more streamlined way to convert back into a string than

<pre><code>NSString* myNewString = [NSString stringWithFormat:@"%d", myInt];
</code></pre>

blocks|key|1728550|text|要真正正确地将字符串转换为数字，需要使用为读取字符串的区域设置配置的NSNumberFormatter实例。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1728551|不同的区域设置会有不同的数字格式。例如，在世界上的一些地方，COMMA被用作小数点分隔符，而在另一些地方，它是PERIOD+- and，千位分隔符(在使用时)被颠倒过来。除非它是一个空格。或者根本不存在。|1728552|这真的取决于输入的来源。最安全的做法是根据输入的格式配置NSNumberFormatter，并使用-[NSFormatter+numberFromString:]从其中获取NSNumber。如果你想处理转换错误，你可以使用-[NSFormatter+getObjectValue:forString:range:error:]。|1728553|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.apple.com/documentation/foundation/nsnumberformatter^0|Y|H|Y|H|0|0|U|5|1J|6|0|S|H|1D|W|2E|8|33|1G|0^^$0|@$1|2|3|4|5|6|7|R|8|@$9|S|A|T|B|C]]|D|@$9|U|A|V|1|W]]|E|$]]|$1|F|3|G|5|6|7|X|8|@$9|Y|A|Z|B|C]|$9|10|A|11|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|12|8|@$9|13|A|14|B|C]|$9|15|A|16|B|C]|$9|17|A|18|B|C]|$9|19|A|1A|B|C]]|D|@]|E|$]]|$1|J|3|-4|5|6|7|1B|8|@]|D|@]|E|$]]]|K|$L|$5|M|N|O|E|$P|Q]]]]

To really convert from a string to a number properly, you need to use an instance of <a href="https://developer.apple.com/documentation/foundation/nsnumberformatter" rel="nofollow noreferrer"><code>NSNumberFormatter</code></a> configured for the locale from which you're reading the string.

Different locales will format numbers differently. For example, in some parts of the world, <code>COMMA</code> is used as a decimal separator while in others it is <code>PERIOD</code> — and the thousands separator (when used) is reversed. Except when it's a space. Or not present at all.

It really depends on the provenance of the input. The safest thing to do is configure an <code>NSNumberFormatter</code> for the way your input is formatted and use <code>-[NSFormatter numberFromString:]</code> to get an <code>NSNumber</code> from it. If you want to handle conversion errors, you can use <code>-[NSFormatter getObjectValue:forString:range:error:]</code> instead.

blocks|key|1513352|text|除了olliej的答案之外，你还可以用NSNumber的stringValue将整型值转换回字符串|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1513353|[[NSNumber+numberWithInt:myInt]+stringValue]|code-block|syntax|javascript|1513354|NSNumber上的stringValue调用descriptionWithLocale:nil，为您提供值的本地化字符串表示。我不确定[NSString+stringWithFormat:@"%25d",myInt]是否会给你一个适当本地化的myInt表示。|1513355|entityMap^0|J|8|S|B|0|0|0|8|A|B|N|P|1W|13|3C|5|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]|$9|13|A|14|B|C]]|D|@]|E|$]]|$1|M|3|-4|5|6|7|15|8|@]|D|@]|E|$]]]|N|$]]

Adding to olliej's answer, you can convert from an int back to a string with <code>NSNumber</code>'s <code>stringValue</code>:

<pre><code>[[NSNumber numberWithInt:myInt] stringValue]
</code></pre>

<code>stringValue</code> on an <code>NSNumber</code> invokes <code>descriptionWithLocale:nil</code>, giving you a localized string representation of value. I'm not sure if <code>[NSString stringWithFormat:@"%d",myInt]</code> will give you a properly localized reprsentation of <code>myInt</code>.

blocks|key|1728722|text|以下是读取本地化数字字符串(xCode+3.2.4，osX+10.6)的NSNumberFormatter的工作示例，以节省我刚才花费的时间。注意:虽然它可以处理诸如"8,765.4“之类的尾随空格，但它不能处理前导空格，也不能处理杂乱的文本字符。(错误的输入字符串："+8“、"8q”和“8q”。)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1728723|NSString+*tempStr+=+@"8,765.4";++
+++++//+localization+allows+other+thousands+separators,+also.
NSNumberFormatter+*+myNumFormatter+=+[[NSNumberFormatter+alloc]+init];
[myNumFormatter+setLocale:[NSLocale+currentLocale]];+//+happen+by+default?
[myNumFormatter+setFormatterBehavior:NSNumberFormatterBehavior10_4];
+++++//+next+line+is+very+important!
[myNumFormatter+setNumberStyle:NSNumberFormatterDecimalStyle];+//+crucial

NSNumber+*tempNum+=+[myNumFormatter+numberFromString:tempStr];
NSLog(@"string+'%25@'+gives+NSNumber+'%25@'+with+intValue+'%25i'",+
++++tempStr,+tempNum,+[tempNum+intValue]);
[myNumFormatter+release];++//+good+citizen|code-block|syntax|javascript|1728724|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Here's a working sample of NSNumberFormatter reading localized number String (xCode 3.2.4, osX 10.6), to save others the hours I've just spent messing around. Beware: while it can handle trailing blanks such as "8,765.4 ", this cannot handle leading white space and this cannot handle stray text characters. (Bad input strings: " 8" and "8q" and "8 q".)

<pre><code>NSString *tempStr = @"8,765.4"; 
 // localization allows other thousands separators, also.
NSNumberFormatter * myNumFormatter = [[NSNumberFormatter alloc] init];
[myNumFormatter setLocale:[NSLocale currentLocale]]; // happen by default?
[myNumFormatter setFormatterBehavior:NSNumberFormatterBehavior10_4];
 // next line is very important!
[myNumFormatter setNumberStyle:NSNumberFormatterDecimalStyle]; // crucial

NSNumber *tempNum = [myNumFormatter numberFromString:tempStr];
NSLog(@"string '%@' gives NSNumber '%@' with intValue '%i'", 
 tempStr, tempNum, [tempNum intValue]);
[myNumFormatter release]; // good citizen
</code></pre>

blocks|key|1513650|text|//+Converting+String+in+to+Double

double+doubleValue+=+[yourString+doubleValue];

//+Converting+Double+in+to+String
NSString+*yourString+=+[NSString+stringWithFormat:@"%25.20f",+doubleValue];
//+.20f+takes+the+value+up+to+20+position+after+decimal

//+Converting+double+to+int

int+intValue+=+(int)+doubleValue;
or
int+intValue+=+[yourString+intValue];|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1513651|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>// Converting String in to Double

double doubleValue = [yourString doubleValue];

// Converting Double in to String
NSString *yourString = [NSString stringWithFormat:@"%.20f", doubleValue];
// .20f takes the value up to 20 position after decimal

// Converting double to int

int intValue = (int) doubleValue;
or
int intValue = [yourString intValue];
</code></pre>

blocks|key|1728849|text|对于从数字到字符串的转换，使用新的文字语法(XCode+>=+4.4)如何，它更紧凑一些。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1728850|int+myInt+=+(int)round(+[@"1.6"+floatValue]+);

NSString*+myString+=+[@(myInt)+description];|code-block|syntax|javascript|1728851|(将其装箱为NSNumber并使用NSObjects'+description+method转换为字符串)|offset|length|1728852|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/Classes/NSNumber_Class/Reference/Reference.html|1|https://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Protocols/NSObject_Protocol/Reference/NSObject.html#//apple_ref/occ/intfm/NSObject/description^0|0|0|6|8|0|H|T|1|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|W|8|@]|9|@$I|X|J|Y|1|Z]|$I|10|J|11|1|12]]|A|$]]|$1|K|3|-4|5|6|7|13|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]|S|$5|N|O|P|A|$Q|T]]]]

For conversion from a number to a string, how about using the new literals syntax (XCode >= 4.4), its a little more compact.

<pre><code>int myInt = (int)round( [@"1.6" floatValue] );

NSString* myString = [@(myInt) description];
</code></pre>

(Boxes it up as a <a href="https://developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/Classes/NSNumber_Class/Reference/Reference.html" rel="nofollow">NSNumber</a> and converts to a string using the <a href="https://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Protocols/NSObject_Protocol/Reference/NSObject.html#//apple_ref/occ/intfm/NSObject/description" rel="nofollow">NSObjects' description method</a>)

blocks|key|1728606|text|为了进行舍入，您可能应该使用math.h中定义的C函数。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1728607|int+roundedX+=+round(x);|code-block|syntax|javascript|1728608|按住Option键并双击Xcode中的round，它将显示一个手册页，其中包含用于对不同类型进行舍入的各种函数。|offset|length|style|CODE|1728609|entityMap^0|0|0|J|5|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]]|$1|G|3|H|5|6|7|Q|8|@$I|R|J|S|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

For rounding, you should probably use the C functions defined in math.h.

<pre><code>int roundedX = round(x);
</code></pre>

Hold down Option and double click on <code>round</code> in Xcode and it will show you the man page with various functions for rounding different types.

blocks|key|1513519|text|这是我所知道的最简单的方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1513520|float+myFloat+=+5.3;
NSInteger+myInt+=+(NSInteger)myFloat;|code-block|syntax|javascript|1513521|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

This is the easiest way I know of:

<pre><code>float myFloat = 5.3;
NSInteger myInt = (NSInteger)myFloat;
</code></pre>

blocks|key|1728787|text|从这里的示例中，您可以看到双向转换：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1728788|NSString+*str=@"5678901234567890";

long+long+verylong;
NSRange+range;
range.length+=+15;
range.location+=+0;

[[NSScanner+scannerWithString:[str+substringWithRange:range]]+scanLongLong:&verylong];

NSLog(@"long+long+value+%25lld",verylong);|code-block|syntax|javascript|1728789|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

from this example here, you can see the the conversions both ways:

<pre><code>NSString *str=@"5678901234567890";

long long verylong;
NSRange range;
range.length = 15;
range.location = 0;

[[NSScanner scannerWithString:[str substringWithRange:range]] scanLongLong:&amp;verylong];

NSLog(@"long long value %lld",verylong);
</code></pre>

blocks|key|1728877|text|我最终使用了这个方便的宏：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1728878|#define+STRING(value)+++++++++++++++[@(value)+stringValue]|code-block|syntax|javascript|1728879|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I ended up using this handy macro:

<pre><code>#define STRING(value) [@(value) stringValue]
</code></pre>

blocks|key|1513764|text|将文本字段中输入的文本转换为整数|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1513765|double+mydouble=[_myTextfield.text+doubleValue];|code-block|syntax|javascript|1513766|四舍五入到最接近的双精度|1513767|mydouble=(round(mydouble));|1513768|四舍五入到最接近的整数(仅考虑正值)|1513769|int+myint=(int)(mydouble);|1513770|从double转换为字符串|1513771|myLabel.text=[NSString+stringWithFormat:@"%25f",mydouble];|1513772|或|1513773|NSString+*mystring=[NSString+stringWithFormat:@"%25f",mydouble];|1513774|从int转换为string|1513775|myLabel.text=[NSString+stringWithFormat:@"%25d",myint];|1513776|1513777|NSString+*mystring=[NSString+stringWithFormat:@"%25f",mydouble];|1513778|entityMap^0|0|0|0|0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|15|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|16|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|17|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|18|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|19|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|1A|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|1B|8|@]|9|@]|A|$]]|$1|Q|3|R|5|D|7|1C|8|@]|9|@]|A|$E|F]]|$1|S|3|T|5|6|7|1D|8|@]|9|@]|A|$]]|$1|U|3|V|5|D|7|1E|8|@]|9|@]|A|$E|F]]|$1|W|3|X|5|6|7|1F|8|@]|9|@]|A|$]]|$1|Y|3|Z|5|D|7|1G|8|@]|9|@]|A|$E|F]]|$1|10|3|T|5|6|7|1H|8|@]|9|@]|A|$]]|$1|11|3|12|5|D|7|1I|8|@]|9|@]|A|$E|F]]|$1|13|3|-4|5|6|7|1J|8|@]|9|@]|A|$]]]|14|$]]

convert text entered in textfield to integer

<pre><code>double mydouble=[_myTextfield.text doubleValue];
</code></pre>

rounding to the nearest double

<pre><code>mydouble=(round(mydouble));
</code></pre>

rounding to the nearest int(considering only positive values)

<pre><code>int myint=(int)(mydouble);
</code></pre>

converting from double to string

<pre><code>myLabel.text=[NSString stringWithFormat:@"%f",mydouble];
</code></pre>

or

<pre><code>NSString *mystring=[NSString stringWithFormat:@"%f",mydouble];
</code></pre>

converting from int to string

<pre><code>myLabel.text=[NSString stringWithFormat:@"%d",myint];
</code></pre>

or

<pre><code>NSString *mystring=[NSString stringWithFormat:@"%f",mydouble];
</code></pre>

I want to convert a string into a double and after doing some math on it, convert it back to a string.

How do I do this in Objective-C?

Is there a way to round a double to the nearest integer too?

How to convert a string into double and vice versa?

Objective-C

Xcode

我想把一个字符串转换成一个双精度型，然后对它做一些数学运算，然后再把它转换回一个字符串。我如何在Objective-C中做到这一点？有没有办法把一个双精度数也舍入到最接近的整数？

问如何将字符串转换为双精度，反之亦然？
EN

回答 11

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问如何将字符串转换为双精度，反之亦然？EN

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问如何将字符串转换为双精度，反之亦然？
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