iphone：float转换为unsigned ints设置为0如果他们是负数？ [英] iphone: floats cast to unsigned ints get set to 0 if they are negative?

问题描述

尝试一下：

volatile float bob = -344.0f;
unsigned int fred = (unsigned int)bob;

printf("%d\n",fred);

输出将为0.

我希望它包装就好像我从一个signed int转换到一个unsgined int（它包装和iphone上的预期行为）

obviously I am expecting it to wrap around just as if I had cast from a signed int to an unsgined int (which does wrap and act as expected on the iphone)

我们假设

推荐答案

这是预期的 - 将一个负浮点数转换为unsigned int会导致未定义的行为（UB）。如果你想要的值wraparound（这也是UB，BTW），那么你需要先转换为一个（signed）int，然后转换为unsigned int。理想情况下，你不应该依靠UB，并找到一个更好的方法来做你需要做的。

This is to be expected - casting a negative float to an unsigned int results in undefined behaviour (UB). If you want the value to wraparound (which is also UB, BTW), then you would need to cast to a (signed) int first and then to unsigned int. Ideally you should not rely on UB at all and find a better way of doing what you need to do.

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