实现一个标准数字字符串四舍五入截取不指定位数的小数

-(NSString *)getFloatStrWithFloatStr:(NSString *)floatStr
                           fixNumber:(NSUInteger)fixNumber
{
    NSLog(@"%.5f, %.f", 5.0/pow(10, fixNumber+1),pow(10, fixNumber+1));
    CGFloat actualAmountValue = [floatStr doubleValue] +5.0/pow(10, fixNumber+1);
    NSString *str1 = [NSString stringWithFormat:@"%.10f",  actualAmountValue];
    NSRange range = [str1 rangeOfString:@"."];
    NSString *newStr = [str1 substringToIndex:range.location+1+fixNumber];
    return newStr;
}      

NSLog(@"%@", [self getFloatStrWithFloatStr:@"123454.690877" fixNumber:3]);