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)num1 num2:(double)num2 { nsdecimalnumber *n1 = [nsdecimalnumber decimalnumberwithstring:[nsstring stringwithformat:@"%f",num1]]; nsdecimalnumber *n2 = [nsdecimalnumber decimalnumberwithstring:[nsstring stringwithformat:@"%f",num2]]; nsdecimalnumber *n3 = [n1 decimalnumberbysubtracting:n2]; return n3.doublevalue; } // 调用: double result = [self decimalnumber: 2.01 num2: 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)number afterpoint:(nsinteger)position { nsdecimalnumberhandler *handler = [nsdecimalnumberhandler decimalnumberhandlerwithroundingmode: nsroundplain scale: position raiseonexactness: no raiseonoverflow: no raiseonunderflow:no raiseondividebyzero: no]; nsdecimalnumber *floatdecimal = [[nsdecimalnumber alloc] initwithfloat: number]; nsdecimalnumber *resultnumber = [floatdecimal decimalnumberbyroundingaccordingtobehavior:handler]; return [nsstring stringwithformat:@"%@",resultnumber]; } // 调用: nsstring *result = [self rounding:8.00092 afterpoint: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nsdecimalnumber api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" @implementation nsdecimalnumber (y_add) + (nsdecimalnumber *)y_decimalnumberwithfloat:(float)value{ return [self y_decimalnumberwithfloat:value scale:2]; } + (nsdecimalnumber *)y_decimalnumberwithfloat:(float)value scale:(short)scale{ return [self y_decimalnumberwithfloat:value roundingmode:nsroundbankers scale:scale]; } + (nsdecimalnumber *)y_decimalnumberwithfloat:(float)value roundingmode:(nsroundingmode)roundingmode scale:(short)scale{ return [[[nsdecimalnumber alloc] initwithfloat:value] y_decimalnumberhandlerwithroundingmode:roundingmode scale:scale]; } + (nsdecimalnumber *)y_decimalnumberwithdouble:(double)value{ return [self y_decimalnumberwithdouble:value scale:2]; } + (nsdecimalnumber *)y_decimalnumberwithdouble:(double)value scale:(short)scale{ return [self y_decimalnumberwithdouble:value roundingmode:nsroundbankers scale:scale]; } + (nsdecimalnumber *)y_decimalnumberwithdouble:(double)value roundingmode:(nsroundingmode)roundingmode scale:(short)scale{ return [[[nsdecimalnumber alloc] initwithfloat:value] y_decimalnumberhandlerwithroundingmode:roundingmode scale:scale]; } /** * <#description#> * * @return <#return value description#> */ - (nsdecimalnumber *)y_decimalnumberhandler{ return [self y_decimalnumberhandlerwithroundingmode:nsroundbankers scale:2]; } - (nsdecimalnumber *)y_decimalnumberhandlerwithroundingmode:(nsroundingmode)roundingmode scale:(short)scale{ nsdecimalnumberhandler *handler = [nsdecimalnumberhandler decimalnumberhandlerwithroundingmode:roundingmode scale:scale raiseonexactness:no raiseonoverflow:yes raiseonunderflow:yes raiseondividebyzero:yes]; return [self decimalnumberbyroundingaccordingtobehavior: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 * * @param number <#number description#> * * @return <#return value description#> */ + (nsstring *)y_formatternumber:(nsnumber *)number{ return [self y_formatternumber:number fractiondigits:2]; } + (nsstring *)y_formatternumber:(nsnumber *)number fractiondigits:(nsuinteger)fractiondigits{ nsnumberformatter *numberformatter = [[nsnumberformatter alloc] init]; [numberformatter setmaximumfractiondigits:fractiondigits]; [numberformatter setminimumfractiondigits:fractiondigits]; return [numberformatter stringfromnumber:number]; }
以上就是本文的全部内容,希望对大家的学习有所帮助,也希望大家多多支持。