reference to non-static member function must be called

今天在LeetCode上做贪心题目时，遇到一个编译错误。

error: reference to non-static member function must be called
sort(g.begin(),g.end(),cmp);

原题是

455. Assign Cookies原题链接

Assume you are an awesome parent and want to give your children some cookies. But, you should give each child at most one cookie.

Each child i has a greed factor g[i], which is the minimum size of a cookie that the child will be content with; and each cookie j has a size s[j]. If s[j] >= g[i], we can assign the cookie j to the child i, and the child i will be content. Your goal is to maximize the number of your content children and output the maximum number.

Example 1:

Input: g = [1,2,3], s = [1,1]
Output:1
Explanation: You have 3 children and 2 cookies. The greed factors of 3 children are 1, 2, 3. 
And even though you have 2 cookies, since their size is both 1, you could only make the child whose greed factor is 1 content.
You need to output 1.

Example 2:

Input: g = [1,2], s = [1,2,3]
Output: 2
Explanation: You have 2 children and 3 cookies. The greed factors of 2 children are 1, 2. 
You have 3 cookies and their sizes are big enough to gratify all of the children, 
You need to output 2.

题目本身不难，一开始写的代码是

class Solution {
public:
     bool cmp(int a,int b)
    {
        return a>b;
    }
    int findContentChildren(vector<int>& g, vector<int>& s) {
        int i=0,j=0;
        int ans=0;
        sort(g.begin(),g.end(),cmp);
        sort(s.begin(),s.end(),cmp);
        while(i<g.size()&&j<s.size()){
            while(i<g.size()&&g[i]>s[j]) i++;
            if(i==g.size()) break;
            ans++;
            i++,j++;
        }
        return ans;
    }
};

但是编译时，出了问题：

执行结果：编译出错
Line 10: Char 32: error: reference to non-static member function must be called
sort(g.begin(),g.end(),cmp);

告诉说是第十行出错了，翻译过来即为

错误：必须调用对非静态成员函数的引用

解决办法即为在cmp函数的返回类型之前加上static关键字。

将com（）定义为static成员函数
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