CODEWITHSUNDEEP
c++sortingstl
StacksAndParsing
StacksAndParsing

Reputation: 119

Sorting a vector of custom objects by one field

If there is a struct:

#include <algorithm>
#include <vector>
#include <iomanip>
#include <string>
using namespace std;

bool pred(string *a, string *b){
    return *a < *b;
}

struct Student {
    int ID;
    int age;
    double gpa;
    string firstname;
    string lastname;
};

int main () {
    vector<Student*>v;
    vector<Student*>v_sortedFirstName;
    //both filled with same information
    // sort v_sortedFirstName by first name
    sort(v_sortedFirstName.begin(), v_sortedFirstName.end(), pred);


}

Now lets say the vector v is filled with information, and v_sortedFirstName is filled with the same information (points to the same spots as v). How would I (using the STL sort function, sort v_sortedFirstName by firstname?

I was thinking this line: sort(v_sortedFirstName.begin(), v_sortedFirstName.end(), pred); should be something along the lines of sort(v_sortedFirstName->firstname.begin(), v_sortedFirstName->firstname.end(), pred); but that doesn't work.

Also, if you guys do not mind, I would like to stick with my predicate function above and not use Lambda as I have not learned that yet.

Upvotes: 0

Views: 652

Answers (1)

Slava
Slava

Reputation: 44258

Your predicate has to accept Student * instead of string *:

bool pred(Student *a, Student *b){
    return a->firtname < b->firtsname;
}

note if you do not intend to modify data change parameters type to const Student * and that would make your code cleaner and safer (if you put code in pred, that by mistake tries to modify that structure then compiler will reject to compile and it would be easy to detect and fix that mistake):

bool pred(const Student *a, const Student *b){
    return a->firtname < b->firtsname;
}

Upvotes: 3

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