!! c运算符，是两个NOT吗？

Question

我读这段代码，并有这行

 switch (!!up + !!left) {

什么是!!运算符？两个逻辑非？

Answer 1

是的，不是两个。!!a是1if a非零，0if a是0您可以将其!!视为钳制{0,1}。我个人觉得这种用法看起来很不好。

Answer 2

您可以这样想象：!(!(a))如果您一步一步做，这很有意义result = !42;    //Result = 0result = !(!42)  //Result = 1 because !0 = 1  这将返回1任何数字（-42、4.2f等），但只有0时会返回result = !0;    //Result = 1result = !(!0)  //result = 0

Answer 3

你是对的。这是两个不。要了解为什么要这样做，请尝试以下代码：#include <stdio.h>int foo(const int a){&nbsp; &nbsp; return !!a;}int main(){&nbsp; &nbsp; const int b = foo(7);&nbsp; &nbsp; printf(&nbsp; &nbsp; &nbsp; &nbsp; "The boolean value is %d, "&nbsp; &nbsp; &nbsp; &nbsp; "where 1 means true and 0 means false.\n",&nbsp; &nbsp; &nbsp; &nbsp; b&nbsp; &nbsp; );&nbsp; &nbsp; return 0;}它输出The boolean value is 1, where 1 means true and 0 means false. 如果删除!!，则输出The boolean value is 7, where 1 means true and 0 means false.