當將浮點數轉換爲int時，爲什麼數字> -1和<-0.5變爲-1，且數字> = -0.5且<0變爲0？

Question

我一直認爲當浮點數被截斷爲整數時，它總是成爲比浮點數小的最大數。但是，當float在-0.5和0之間時，它將轉換爲0而不是-1！爲什麼是這樣？這是語言特定的嗎？我在objC看到這個。

Answer 1

嗯，簡單的答案是，你的理解實際上是正確的：

0比-1的數量更多。

更長或更詳細的答案取決於如何將浮點數轉換爲整數。如果你想爲「0.5」浮點數而不是「0」，你可能需要編寫你自己的實現方案，將負數從浮點數中除去，將其向上或向下取整爲一個整數，然後添加（或相乘。-1，要準確）的負號返回到它

這裏有一些代碼我寫的演示中實現的差異：

#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中，結果出來的：

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