STL函数对象

#include "../std_lib_facilities.h"
struct Record {
    string firstname;
    char* lastname;
    Record(string s, char* p) :firstname(s), lastname(p) {}
    void print() { cout << firstname << " " << lastname <<'\n'; }
};
bool f(Record& r) { return r.firstname == "Diana"; } //函数当作参数传递
struct cmp_fname {    //函数对象
    bool operator()(const Record& a,const Record& b)const
    {
        return a.firstname < b.firstname;
    }
};
/*struct cmp_lname  {
    bool operator()(const Record& a, const Record& b)const
    {
        return strncmp(a.lastname, b.lastname,20) < 0;
    }
};*/
bool cmp_lname(const Record& a, const Record& b)
{
    return strncmp(a.lastname, b.lastname, 20) < 0;
}
int main(){
    vector<Record> vr = { 
Record{"Arthur","Curry"},
Record{"Barry","Allen"},
Record{"Diana","Prince"},
Record{"Clark","Kent"}
 };
    cout << "sort by first name:" << '\n';
    cout << "--------------------------" << '\n';
    sort(vr.begin(), vr.end(), cmp_fname()); //注意 cmp_fname()括号
    for (auto r : vr)
        r.print();
    cout <<'\n'<< "sort by last name:" << '\n';
    cout << "--------------------------" << '\n';
    sort(vr.begin(), vr.end(), cmp_lname);
    for (auto r : vr)
        r.print();
    cout << "--------------------------" << '\n';
    auto p=find_if(vr.begin(), vr.end(), f); //做参数时不要加()，会变成函数调用
    cout << "position " << p - vr.begin() + 1 << endl;
    system("pause");
    return 0;
}

输出:

sort by first name:
--------------------------
Arthur Curry
Barry Allen
Clark Kent
Diana Prince

sort by last name:
--------------------------
Barry Allen
Arthur Curry
Clark Kent
Diana Prince
--------------------------
position 4
请按任意键继续. . .