objective-c - 将 float 转换为 int 时，为什么数字 > -1 和 < -0.5 变为 -1，而数字 >= -0.5 和 < 0 变为 0？

Question

我一直认为当浮点数被截断为整数时，它总是成为小于浮点数的最大数字。但是，当浮点数介于 -0.5 和 0 之间时，它会转换为 0 而不是 -1！为什么是这样？这是特定于语言的吗？我在 objC 中看到了这一点。

Answer 1

好吧，简短的回答是您的理解实际上是正确的：

0 是大于 -1 的数字。

更长或更详细的答案取决于如何将浮点数转换为整数。如果您想要“0.5”的浮点数使用“-1”而不是“0”，您可能需要编写自己的实现，将负数从浮点数中去除，将其向上或向下舍入为整数，然后相加（或相乘） a -1，准确地说）负号回到它上面。

这是我为演示实现差异而编写的一些代码：

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[])
{

    @autoreleasepool {

        // insert code here...
        NSLog(@"Hello, World!");
        float floatNumber = -1.0f;
        for(NSInteger index = 0; index < 20; index++)
        {
            NSLog( @"floatNumber is %4.2f and integer is %d %d", floatNumber, (int) floatNumber, (int)roundf(floatNumber));
            floatNumber+=0.1f;
        }
    }
    return 0;
}

在 Xcode 下，结果如下：

floatNumber is -1.00 and integer is -1 -1
floatNumber is -0.90 and integer is 0 -1
floatNumber is -0.80 and integer is 0 -1
floatNumber is -0.70 and integer is 0 -1
floatNumber is -0.60 and integer is 0 -1
floatNumber is -0.50 and integer is 0 0
floatNumber is -0.40 and integer is 0 0
floatNumber is -0.30 and integer is 0 0
floatNumber is -0.20 and integer is 0 0
floatNumber is -0.10 and integer is 0 0
floatNumber is 0.00 and integer is 0 0
floatNumber is 0.10 and integer is 0 0
floatNumber is 0.20 and integer is 0 0
floatNumber is 0.30 and integer is 0 0
floatNumber is 0.40 and integer is 0 0
floatNumber is 0.50 and integer is 0 1
floatNumber is 0.60 and integer is 0 1
floatNumber is 0.70 and integer is 0 1
floatNumber is 0.80 and integer is 0 1
floatNumber is 0.90 and integer is 0 1