Sorting a vector with pointer at object C++ - c++

Question

If anyone can help I would be very grateful.
How do i sort this vector:
vector<Person*>person
by this criterium:
Surname
I have already tried it using set but it removes object if there is more than 2 objects with same Surname
there are lot of string variables, and I need to sort it by
Surname
and then if surnames are the same, then I need to sort them by
Name
and also it sorts by hexadecimal value of that pointer...
EDIT:
More code as you ask:
for (pChild = pRoot->FirstChildElement("Member"); pChild != NULL; pChild = pChild->NextSiblingElement())
{
string Surname = pChild->Attribute("surname");
string Name = pChild->Attribute("name");
string DateOfBirth = pChild->Attribute("dateofbirth");
person.push_back(new Person(Surname, Name, DateOfBirth));
}

Answer 1

Without you showing more of your code, it is hard to help you, but I would look at the documentation for std::sort() as you can create custom operators to sort your vector.

Answer 2

Here's a complete example
#include <vector>
#include <iostream>
#include <algorithm>
class Person
{
public:
std::string s1, s2, s3;
Person(std::string S1, std::string S2, std::string S3) : s1(S1), s2(S2), s3(S3) {}
};
struct less_than_key
{
inline bool operator() (const Person* const p1, const Person* const p2)
{
if (p1->s1 < p2->s1)
return true;
else if (p1->s1 == p2->s1 && p1->s2 < p2->s2)
return true;
return false;
}
};
int main()
{
std::vector<Person*> persons{ new Person("C", "D", "E"), new Person("C", "C", "D"),
new Person("B", "C", "D"), new Person("B", "C", "E")};
std::sort(persons.begin(), persons.end(), less_than_key());
for (auto person : persons)
{
std::cout << person->s1 << ' ' << person->s2 << std::endl;
}
return 0;
}

Answer 3

I had a bit of fun doing it with std::set. There are a couple of examples of comparators. One function and one "functor."
#include <iostream>
#include <set>
#include <string>
struct Person {
uint64_t id;
std::string name;
std::string family_name;
bool operator<(const Person &other) const {
if (family_name == other.family_name) {
if (name == other.name) {
return id < other.id;
} else {
return name < other.name;
}
} else {
return family_name < other.family_name;
}
}
};
std::ostream &operator<<(std::ostream &os, const Person &x) {
return os << '{' << x.id << ", " << x.name << ", " << x.family_name << '}';
}
bool person_ptr_less(const Person *a, const Person *b) { return *a < *b; }
class PersonPtrComparator {
public:
bool operator()(const Person *a, const Person *b) const { return *a < *b; }
};
int main() {
std::set<Person *, bool (*)(const Person *, const Person *)> people(
person_ptr_less);
people.emplace(new Person{1, "Joe", "Smith"});
people.emplace(new Person{2, "Joe", "Blow"});
people.emplace(new Person{3, "Joa", "Smith"});
people.emplace(new Person{4, "Joe", "Smith"});
std::set<Person *, PersonPtrComparator> people_2(people.begin(),
people.end());
for (const auto &x : people) {
std::cout << *x << '\n';
}
std::cout << "---\n";
for (const auto &x : people_2) {
std::cout << *x << '\n';
}
return 0;
}

Answer 4

You can use a comparator like this:
// Simple class
class Person {
public:
string name;
Person(string name) {
this->name = name;
}
};
// create a comparator like this with two objects as parameters.
bool comparator(Person* a, Person *b) {
return a->name > b->name;
}
int main() {
vector<Person* > v;
v.push_back(new Person("ajay"));
v.push_back(new Person("tanya"));
// pass the comparator created into sort function.
sort(v.begin(), v.end(),comparator);
// printing output to check
for(int i=0;i<v.size();i++) {
cout<<v[i]->name<<endl;
}
}