详解iOS之关于double/float数据计算精度问题
1、我们的app有一个判断,当用户输入的值,小于等于剩余的余额时,给用户弹窗,代码不往下执行
当用户输入0.01时,po一下的结果是:0.10000....,当用户的余额是0.01时,po一下网络请求的返回结果是:0.009999...
当用户输入66.05时,po 一下的结果是:66.049999...,当用户的余额是66.05时,po一下网络请求的返回结果是:66.049999...
所以,当数据较大时,不会有影响,因为用户输入的数据和网络返回数据都被变成了不精确的小值了;但是,当数据较小时,用户输入的数据没有被转,网络返回的数据被转成了不精确的小值,导致用户输入永远大于网络返回的数据,代码无法往下执行;
解决:使用NSDecimalNumber将float、double数据转化成NSDecimalNumber类型的对象进行+、-、*、/计算,再取值。
-(double)DecimalNumber:(double)num1num2:(double)num2{ NSDecimalNumber*n1=[NSDecimalNumberdecimalNumberWithString:[NSStringstringWithFormat:@"%f",num1]]; NSDecimalNumber*n2=[NSDecimalNumberdecimalNumberWithString:[NSStringstringWithFormat:@"%f",num2]]; NSDecimalNumber*n3=[n1decimalNumberBySubtracting:n2]; returnn3.doubleValue; } //调用: doubleresult=[selfDecimalNumber:2.01num2:2];//结果为0.01
其中:
decimalNumberBySubtracting:n1-n2,返回n1-n2的结果值
decimalNumberByMultiplyingBy:n1*n2,
decimalNumberByDividingBy:n1/n2,
decimalNumberByAdding:n1+n2,
compare:比较n1和n2,返回比较结果;
2、进行数据的四舍五入获得结果
-(NSString*)Rounding:(float)numberafterPoint:(NSInteger)position { NSDecimalNumberHandler*handler=[NSDecimalNumberHandlerdecimalNumberHandlerWithRoundingMode:NSRoundPlainscale:positionraiseOnExactness:NOraiseOnOverflow:NOraiseOnUnderflow:NOraiseOnDivideByZero:NO]; NSDecimalNumber*floatDecimal=[[NSDecimalNumberalloc]initWithFloat:number]; NSDecimalNumber*resultNumber=[floatDecimaldecimalNumberByRoundingAccordingToBehavior:handler]; return[NSStringstringWithFormat:@"%@",resultNumber]; } //调用: NSString*result=[selfRounding:8.00092afterPoint:3];//结果为8.001
其中,参数number是需要四舍五入的数据,position是小数点后保留的位数;
高精度要求
使用系统提供的NSDecimalNumberAPI进行计算,最后转换为字符串输出显示。NSDecimalNumber转换方法:
#import"NSDecimalNumber+Y_Add.h" @implementationNSDecimalNumber(Y_Add) +(NSDecimalNumber*)y_decimalNumberWithFloat:(float)value{ return[selfy_decimalNumberWithFloat:valuescale:2]; } +(NSDecimalNumber*)y_decimalNumberWithFloat:(float)valuescale:(short)scale{ return[selfy_decimalNumberWithFloat:valueroundingMode:NSRoundBankersscale:scale]; } +(NSDecimalNumber*)y_decimalNumberWithFloat:(float)valueroundingMode:(NSRoundingMode)roundingModescale:(short)scale{ return[[[NSDecimalNumberalloc]initWithFloat:value]y_decimalNumberHandlerWithRoundingMode:roundingModescale:scale]; } +(NSDecimalNumber*)y_decimalNumberWithDouble:(double)value{ return[selfy_decimalNumberWithDouble:valuescale:2]; } +(NSDecimalNumber*)y_decimalNumberWithDouble:(double)valuescale:(short)scale{ return[selfy_decimalNumberWithDouble:valueroundingMode:NSRoundBankersscale:scale]; } +(NSDecimalNumber*)y_decimalNumberWithDouble:(double)valueroundingMode:(NSRoundingMode)roundingModescale:(short)scale{ return[[[NSDecimalNumberalloc]initWithFloat:value]y_decimalNumberHandlerWithRoundingMode:roundingModescale:scale]; } /** *<#Description#> * *@return<#returnvaluedescription#> */ -(NSDecimalNumber*)y_decimalNumberHandler{ return[selfy_decimalNumberHandlerWithRoundingMode:NSRoundBankersscale:2]; } -(NSDecimalNumber*)y_decimalNumberHandlerWithRoundingMode:(NSRoundingMode)roundingModescale:(short)scale{ NSDecimalNumberHandler*handler=[NSDecimalNumberHandlerdecimalNumberHandlerWithRoundingMode:roundingMode scale:scale raiseOnExactness:NO raiseOnOverflow:YES raiseOnUnderflow:YES raiseOnDivideByZero:YES]; return[selfdecimalNumberByRoundingAccordingToBehavior:handler]; } @end
普通精度要求
使用系统提供的数学运算进行计算,最后转换为字符串输出显示。保留小数点后N位的方法:
/** *formatterNumber.00小数点后两位 * *@paramnumber<#numberdescription#> * *@return<#returnvaluedescription#> */ +(NSString*)y_formatterNumber:(NSNumber*)number{ return[selfy_formatterNumber:numberfractionDigits:2]; } +(NSString*)y_formatterNumber:(NSNumber*)numberfractionDigits:(NSUInteger)fractionDigits{ NSNumberFormatter*numberFormatter=[[NSNumberFormatteralloc]init]; [numberFormattersetMaximumFractionDigits:fractionDigits]; [numberFormattersetMinimumFractionDigits:fractionDigits]; return[numberFormatterstringFromNumber:number]; }
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