struct mycompare和static bool mycompare有什么区别？

struct mycompare1 {
    bool operator() (const Interval a, const Interval b) {
        return a.start < b.start;
    }
} mycompare1_instance;

static bool mycompare2(const Interval a, const Interval b) {
    return a.start < b.start;
}

Q1: What is the difference between these two. It seems that mycompare1_instance somehow equals to mycompare2 like this. The following two lines seem to do the same thing.

Q1：这两者之间有什么区别。似乎mycompare1_instance在某种程度上等于mycompare2就像这样。以下两行似乎也做同样的事情。

sort(intervals.begin(), intervals.end(), mycompare1);
sort(intervals.begin(), intervals.end(), mycompare2);

Could anyone explain it?

谁能解释一下呢？

Q2: How is "static" useful here?

Q2：这里的“静态”有用吗？

Thx ahead!

先生！

2 个解决方案

#1

The first case defines operator() so you could could use it as a function - in short they are functors. The advantage is that it can have a state and depending how you define the operator() you could use the instance of that class as a function. Thse second case is simply a static functionn and does not hold the state in the sense of a class/struct.

第一种情况定义了operator（），因此您可以将它用作函数 - 简而言之它们是函子。优点是它可以具有状态，并且取决于您如何定义operator（），您可以将该类的实例用作函数。第二种情况只是一个静态函数，并不保持类/结构意义上的状态。

#2

I suspect the question is related to functors

我怀疑这个问题与仿函数有关

ie you have seen

即你见过

mycompare_instance1(x,y)

mycompare2(x,y)

The first one is a functor. It used where we need to make things that are both objects with state and can be invoked like functions. The second one is a simple function

第一个是仿函数。它用于我们需要制作既是状态对象又可以像函数一样调用的东西。第二个是一个简单的功能

#1

#2