在目标c中浮动的字符串 [英] String to float in objective c

问题描述

我有一个方法要求两个NSString和一个浮点数值，但我不能将字符串转换为浮动，这是我的代码：

$ p $ N $ ] initWithString：@EUR];
NSString * to = [[NSString alloc] initWithString：[attributeDict objectForKey：@currency]];
NSNumber * rate = [[NSNumber alloc] initWithFloat：[[attributeDict objectForKey：@rate] doubleValue]];


currency = [[Currency init] alloc];
[currency addCurrencyWithFrom：from andTo：to andRate：rate];

在.h

   - （id）addCurrencyWithFrom：（NSString *）from_和To：（NSString *）to_ andRate：（float *）float_; 
  

解决方案

No no no no no no no no no no。

使用 NSNumberFormatter 。这就是为什么它存在。 -floatValue 和 -doubleValue 只是快捷方便的临时修复，但是它们会以不好的方式失败。例如：

  NSLog（@％f，[@123floatValue]）; //日志123.0000 
 NSLog（@％f，[@abcfloatValue]）; //日志0.0000 
 NSLog（@％f，[@0floatValue]）; //日志0.0000 
 NSLog（@％f，[@42floatValue]）; // log 42.0000 
 NSLog（@％f，[@42xfloatValue]）; // log 42.0000 
  

-floatValue is unable （ @0）和一个无效的（ @abc）区分。 / p>

NSNumberFormatter ，另一方面会给你 nil 如果它不能解析它，并且如果可以的话 NSNumber 。它还需要像货币符号，区域特定的小数和千位分隔符以及用户的区域设置。 -floatValue 和朋友不需要。

有关详细信息，请参阅以下相关问题：

$ b $

b

I have a parser returning some string value I'd like to use as parameter for my class instance initialisation.

I have a method asking two NSString and a float value, but I can't convert the string to float, here is my code:

 NSString *from = [[NSString alloc] initWithString:@"EUR"];
    NSString *to = [[NSString alloc] initWithString:[attributeDict objectForKey:@"currency"]];
    NSNumber *rate = [[NSNumber alloc] initWithFloat:[[attributeDict objectForKey:@"rate"] doubleValue]];


   currency = [[Currency init] alloc];
   [currency addCurrencyWithFrom:from andTo:to andRate:rate];

in the .h

- (id) addCurrencyWithFrom: (NSString *) from_ andTo:(NSString *) to_ andRate:(float *) float_;

解决方案

No no no no no no no no no.

Use an NSNumberFormatter. This is why it exists. -floatValue and -doubleValue are merely quick-and-easy temporary fixes, but they fail in bad ways. For example:

NSLog(@"%f", [@"123" floatValue]); //logs 123.0000
NSLog(@"%f", [@"abc" floatValue]); //logs 0.0000
NSLog(@"%f", [@"0" floatValue]);   //logs 0.0000
NSLog(@"%f", [@"42" floatValue]);  //logs 42.0000
NSLog(@"%f", [@"42x" floatValue]); //logs 42.0000

-floatValue is unable to distinguish between a proper number (@"0") and an invalid one (@"abc").

NSNumberFormatter, on the other hand, will give you nil if it can't parse it, and an NSNumber if it can. It also takes things like currency symbols, region-specific decimal and thousands separators, and the user's locale into account. -floatValue and friends do not.

See this related question for more info: How to convert an NSString into an NSNumber

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