与NSUInteger奇怪的行为 - 不能转换为浮动正确 [英] Odd behavior with NSUInteger - can't convert to float properly

问题描述

下面是我的情况。它的驾驶我坚果：

我有一个NSMutableArray与517的计数值我有一个double值我的倍增器。

 双乘数= 0.1223;
double结果= [myArray的数] *乘数; // 63连（错了！）
 

在事实上，它应该是63.2291。如果我去：

 双重结果= [myArray的数] * 0.1223; // 63.2291（右！）
 

或..

 双重结果= 517 *乘数; // 63.2291（右！）
 

这是否任何意义，任何人吗？

附录：

这是我的实际功能：

   - （双）getValueForPercentage：（双）percVal
{
   INT adjustedCount = [originalData数]  -  1;
   双打决赛= percVal *（双）adjustedCount;
   最终回报;
}
 

我的从不的得到任何的数字超出了小数点当我这样做。它的确实的工作，但是如果我摆脱了-1，一拉：

   - （双）getValueForPercentage：（双）percVal
{
   INT adjustedCount = [originalData计数]
   双打决赛= percVal *（双）adjustedCount;
   最终回报;
}
 

当然，我需要有-1。

二编：

我注意到另一个有趣的事情是，如果我通过一个硬codeD编号给这个函数它工作正常，但如果我通过，我需要使用双重价值，它失败：

  INT pointCount = [srcData getDayCount]的for（int i = 0; I＆LT; pointCount;我++）{
   双进度=（双）I /（双）（pointCount  -  1）;
   双SATV = [srcData getValueForPercentage：进展]
   // SATV是始终没有超越小数位数的任何一个数字
}
 

解决方案

好吧，当我开始有这些问题，我四处张望了一下，发现没有任何理由或解释。

我现在要做的就是让一切都成为一个NSNumber，然后调用的doubleValue就可以了。这应该得到你正在寻找的结果：

 的NSNumber * pointCount = [NSNumber的numberWithUnsignedInt：[srcData getDayCount]];
为（NSInteger的I = 0; I＆下; [pointCount的intValue];我++）{
    *的NSNumber数= [NSNumber的numberWithInt：我]。
    双进度= [计数的doubleValue] / [pointCount的doubleValue]  -  1.0;
    双SATV = [srcData getValueForPercentage：进展]
    // SATV是始终没有超越小数位数的任何一个数字
}
 

希望它帮助。

Here is my situation. Its driving me nuts:

I have an NSMutableArray with a count value of 517. I have a double value that is my multiplier.

double multiplier = 0.1223;
double result = [myArray count] * multiplier; // 63 even (wrong!)

In fact it should be 63.2291. If I go:

double result = [myArray count] * 0.1223; // 63.2291 (right!)

or..

double result = 517 * multiplier; // 63.2291 (right!)

Does this make any sense to anyone?

Addendum:

here is my actual function:

- (double) getValueForPercentage:(double)percVal
{
   int adjustedCount = [originalData count] - 1;
   double final = percVal * (double)adjustedCount;
   return final;
}

I never get any digits beyond the decimal point when I do this. It does however work if I get rid of the "-1", a-la:

- (double) getValueForPercentage:(double)percVal
{
   int adjustedCount = [originalData count];
   double final = percVal * (double)adjustedCount;
   return final;
}

Of course, I need to have the -1.

Second addendum:

Another interesting thing I noted was, if I pass a hard-coded number to this function it works fine, but if I pass the double value that I need to use, it fails:

int pointCount = [srcData getDayCount];

for (int i = 0; i < pointCount; i++) {
   double progress = (double)i/(double)(pointCount - 1);
   double satv = [srcData getValueForPercentage:progress];
   // satv is always a number without any digits beyond the decimal
}

解决方案

Well, when I started to have these issues i looked around a bit and found no reason or explanation.

What I do now is make everything become an NSNumber and then call doubleValue on it. This should yield the results you're looking for:

NSNumber * pointCount = [NSNumber numberWithUnsignedInt: [srcData getDayCount]];
for (NSInteger i = 0; i < [pointCount intValue]; i++) {
    NSNumber * count = [ NSNumber numberWithInt: i ];
    double progress = [count doubleValue]/[pointCount doubleValue] - 1.0;
    double satv = [srcData getValueForPercentage:progress];
    // satv is always a number without any digits beyond the decimal
}

Hope it helps.

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