In this article, we will see how to initialize and use vector of structs in C++.
There are different ways to do it. This article will explain these methods clearly.
Table of Contents
Using Range Constructor
We can utilize the range constructor for the initialization of vector of structs in C++. It is useful when we need to make another copy of the existing vector. We will declare a different vector and copy the elements from the old vector using the range. We can access the elements of structs using ‘struct.element’ at the time of output.
Code:
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#include <iostream> #include <string> #include <vector> using namespace std; //Initializing Structure: Student struct Student{ string first_name; string last_name; int roll_no; }; int main(){ //creating vector of structure(Student) vector<Student> stu1 = {{"Steve", "Smith", 59}, {"Shane", "Watson", 57}, {"Adam", "Gilchrist", 3}, {"Ricky", "Ponting", 43}}; //Passing the range of vector stu1 from first to last position //Creating another copy of vector stu1 vector<Student> new_stu(stu1.begin(), stu1.end()); //Printing the new vector for (const auto &arr : new_stu) { cout << "First Name: " << arr.first_name << endl << "Last Name: " << arr.last_name << endl << "Roll Number: " << arr.roll_no << endl; } return 0; } |
Output
Last Name: Smith
Roll Number: 59
First Name: Shane
Last Name: Watson
Roll Number: 57
First Name: Adam
Last Name: Gilchrist
Roll Number: 3
First Name: Ricky
Last Name: Ponting
Roll Number: 43
Further reading:
Using Initializer list
It is a simple method to create a vector of structs in C++. Here we initialize the container with the constant values. This method is better when it is important to have an initial state of some type for data structure.
Code:
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#include <iostream> #include <string> #include <vector> using namespace std; //Initializing Structure: Student struct Student{ string first_name; string last_name; int roll_no; }; int main(){ //creating vector of structure(Student) vector<Student> stu1 = {{"Steve", "Smith", 59}, {"Shane", "Watson", 57}, {"Adam", "Gilchrist", 3}, {"Ricky", "Ponting", 43}}; //Printing the vector for (const auto &arr : stu1) { cout << "First Name: " << arr.first_name << endl << "Last Name: " << arr.last_name << endl << "Roll Number: " << arr.roll_no << endl; } return 0; } |
Output
Last Name: Smith
Roll Number: 59
First Name: Shane
Last Name: Watson
Roll Number: 57
First Name: Adam
Last Name: Gilchrist
Roll Number: 3
First Name: Ricky
Last Name: Ponting
Roll Number: 43
Using custom constructor
In this method, we create a vector specific constructor which will initialize the vector with a given number filled with different values. Here we will take input from the user and we create a custom vector of structs with different values.
Code:
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#include <iostream> #include <string> #include <vector> using namespace std; struct Student{ string first_name; string last_name; int age; }; constexpr int count1 = 2; int main(){ //Custom Constructor to print the same values number of times vector<Student> stu1(count1, {"Donald", "Bradman", 32}); //Custom constructor to take complete input from the user vector<Student> stu2; Student p; int count; cout<<"Enter the number of values you want to add:"; cin>>count; for(int i = 0; i < count; ++i) { cout << "Please enter the first name, last name and roll number of a student:" << endl; string first_name, last_name; int age1; cin >> first_name; cin >> last_name; cin >> age1; p.first_name=first_name; p.last_name=last_name; p.age=age1; stu2.push_back(p);//Adding elements in the vector } //Printing the vector stu1 cout<<"\nFirst Vector\n"; for (const auto &arr1 : stu1) { cout << "First Name: " << arr1.first_name << endl << "Last Name: " << arr1.last_name << endl << "Age: " << arr1.age << endl; } //Printing the vector stu2 cout<<"\nSecond Vector:\n"; for (const auto &arr1 : stu2) { cout << "First Name: " << arr1.first_name << endl << "Last Name: " << arr1.last_name << endl << "Age: " << arr1.age << endl; } return 0; } |
Input
Please enter the first name, last name and roll number of a student:
Glenn
Maxwell
30
Please enter the first name, last name and roll number of a student:
David
Warner
21
Output
First Name: Donald
Last Name: Bradman
Age: 32
First Name: Donald
Last Name: Bradman
Age: 32
Second Vector:
First Name: Glenn
Last Name: Maxwell
Age: 30
First Name: David
Last Name: Warner
Age: 21
Bonus Program
Program to sort a vector of structs in C++ according to the roll numbers of the students.
Code
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#include <iostream> #include <vector> #include <algorithm> using namespace std; //Intializing struct struct Student { int roll_no; string student_name; }; //Printing the vector void Print(vector<Student>& vect1) { for (int i = 0; i < vect1.size(); ++i) { cout << vect1[i].roll_no << ' ' << vect1[i].student_name << endl; } cout << endl; } int main() { //Filling values in the vector of student(struct) type vector<Student> vect; vect.push_back({ 72, "Louis" }); vect.push_back({ 78, "Mike" }); vect.push_back({ 26, "Harvey" }); vect.push_back({ 15, "David" }); cout << "Original Vector Before Sorting:\n" << endl; Print(vect); //Sorting ascendigly according to the roll number sort(vect.begin(), vect.end(), [](Student a, Student b) { return a.roll_no < b.roll_no; }); cout << "Vector After Sorting:\n" << endl; Print(vect); return 0; } |
Output
72 Louis
78 Mike
26 Harvey
15 David
Vector After Sorting:
15 David
26 Harvey
72 Louis
78 Mike
Conclusion
In this article we demonstrated different methods that can create a vector of structs in C++. Custom Constructor method can be used in other ways as well as per the needs of the program.
Happy Learning!!
