(4 > y > 1) 是 C++ 中的有效语句吗?如果有，你如何评价?
这是一个有效的表达吗?如果是这样，您能否重写它以使其更有意义?例如，它是否与 (4 > y && y > 1) 相同?您如何评估链式逻辑运算符?
Is that a valid expression? If so, can you rewrite it so that it makes more sense? For example, is it the same as (4 > y && y > 1)? How do you evaluate chained logical operators?
推荐答案
语句 (4 > y > 1) 解析如下:
((4 > y) > 1)
比较运算符 < 和 > 从左到右评估.
The comparison operators < and > evaluate left-to-right.
4 >y 返回 0 或 1 取决于它是否为真.
The 4 > y returns either 0 or 1 depending on if it's true or not.
然后将结果与 1 进行比较.
Then the result is compared to 1.
在这种情况下，由于0或1永远不会超过1，整个语句将始终返回false.
In this case, since 0 or 1 is never more than 1, the whole statement will always return false.
不过有一个例外:
如果 y 是一个类并且 > 运算符已被重载以执行不寻常的操作.然后一切顺利.
If y is a class and the > operator has been overloaded to do something unusual. Then anything goes.
例如，这将无法编译:
class mytype{
};
mytype operator>(int x,const mytype &y){
return mytype();
}
int main(){
mytype y;
cout << (4 > y > 1) << endl;
return 0;
}
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