C ++排序：找不到匹配的重载函数

Question

我正在尝试通过使用自定义比较函数对其调用sort来对结构向量进行排序。

以下是比较和排序功能：

bool Patient::compareByTime(const event &a, const event &b) {
    time_t atime, btime; 
    atime = a.timestamp;
    btime = b.timestamp;
    return (difftime(atime, btime) > 0);
}

void Patient::calculateStays() {

    sort(events.begin(), events.end(), compareByTime);

}

以下是头文件中的struct和vector声明：

class Patient
{   
    //some stuff omitted here...

    struct event {
        string facility;
        string inpeme;
        string complaint;
        string admidisc;
        time_t timestamp = 0;
    };
    vector<event> events;


public: 

   //some stuff omitted here... 

    bool compareByTime(const event &a, const event &b);
    void calculateStays();

};

这些是我无法解决的错误：

'Patient::compareByTime': non-standard syntax; use '&' to create a pointer to member
'sort': no matching overloaded function found
'void std::sort(const _RanIt,const _RanIt)': expects 2 arguments - 3 provided