c# - 表达式 `?`中的符号 `maxY = (maxY > pt.Y) ? maxY : pt.Y;`是什么意思

Question

符号?在下面的代码中是什么意思:

  for(int i = 0 ; i < Hpts.BranchCount;i++)
    { foreach(Point3d pr in Hpts.Branches[i]){
        minX = (minX > pt.X) ? pt.X : minX;
        minY = (minY > pt.Y) ? pt.Y : minX;
        maxX = (maxX > pt.X) ? maxX : pt.X;
        maxY = (maxY > pt.Y) ? maxY : pt.Y;
      }
    }

Answer 1

它被称为条件运算符。参见documentation

The conditional operator (?:) returns one of two values depending on the value of a Boolean expression. Following is the syntax for the conditional operator.

condition ? first_expression : second_expression;

The condition must evaluate to true or false. If condition is true, first_expression is evaluated and becomes the result. If condition is false, second_expression is evaluated and becomes the result. Only one of the two expressions is evaluated.

以你的情况为例:

minX = (minX > pt.X) ? pt.X : minX;

• minX > pt.X 是条件
• pt.X 是 first_expression
• minX 是second_expression

这意味着如果条件为true，minX 的值将等于pt.X，否则它不会改变，因为第二个表达式本身就是变量。