比较objective C中的浮动和双数据类型

When using double or float data type in an iPhone app, I am running into problems with ">=" and "<=" comparisons because when a variable is assigned a number entered with one decimal place, such as 4.2, the float or double used in the comparison actually may have a value such as 4.1999998092651367. Because of this difference, a comparison such as ">= 4.2" is false instead of true. How can I avoid this problem?

当使用双或浮点数据类型在一个iPhone应用程序,我遇到问题“> =”、“< =”比较,因为当一个变量被分配一个号码进入一个小数位,如4.2中,使用的浮点数和双精度数比较实际值如4.1999998092651367。由于这种差异，像“>= 4.2”这样的比较是假的而不是真的。我怎样才能避免这个问题呢?

1 个解决方案

#1

when a variable is assigned a number entered with one decimal place, such as 4.2, the float or double used in the comparison actually may have a value such as 4.1999998092651367

当一个变量被赋值为一个小数时，例如4.2，比较中使用的浮点数或双精度数实际上可能有一个值，比如4.1999998092651367

Not may. will. To be specific:

不可能。会的。具体的说:

float f = 4.2;  // f is exactly 4.19999980926513671875
double d = 4.2; // d is exactly 4.20000000000000017763568394002504646778106689453125

The problem comes when you write something like:

当你写这样的东西时，问题就来了:

float f = 4.2;
if (f >= 4.2) {
    // this block of code is not executed.
}

f is exactly 4.19999980926513671875, but you're comparing it to the double-precision literal "4.2", which has the value 4.20000000000000017763568394002504646778106689453125, so the comparison fails. If instead you compare against the single precision literal "4.2f":

f正好是4.19999980926513671875，但是您将它与双精度文字“4.2”进行比较，后者的值是4.20000000000000000001776356839400400467786689453125，所以比较失败。如果你把它与单精度文字“4.2f”进行比较:

float f = 4.2;
if (f >= 4.2f) {
    // this block of code is exectued.
}

the comparison succeeds, because the values are exactly equal. Floating-point is complicated, but it is entirely deterministic; one of the simplest things you can do to make it more intuitive is to not mix precisions. If you're working with float, make sure all of your literals are suffixed with f to make them single precision, too.

比较成功，因为值完全相等。浮点是复杂的，但完全是确定性的;要使它更直观，最简单的事情之一就是不要混淆精确。如果使用浮点数，请确保所有的字符都以f结尾，以使它们也具有单一的精度。

(This can also improve performance, but that's not the reason to do it; the reason to do it is because it will make your code more correct).

(这也可以提高性能，但这不是这么做的原因;这样做的原因是它将使您的代码更加正确)。

#1