C++ Standard Template Library (STL) – [Vector]

A vector is a data structure for maintaining a set of elements having a specific data type. Vectors can be considered as arrays having dynamic size. Just like arrays, vectors also store its elements in a contiguous storage locations. That is why, elements in a vector can be accessed using offsets or regular pointers to its elements.

Although vectors can dynamically increase their size, a vector need not allocate extra storage, every time an element is added to it. This is because a vector may have an actual capacity greater than the storage strictly needed to contain its elements (i.e., its size). Different libraries can implement different strategies for increased size to balance between memory usage and reallocations.

To use STL built-in vector, you need to include <vector> header.

Code
//
//  main.cpp
//  Vector (STL)
//
//  Created by Himanshu on 23/09/21.
//

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

void printIntVector (vector<int> l) {
    vector<int>::iterator it;
    for (it = l.begin(); it != l.end(); it++) {
        cout<<(*it)<<" ";
    }
    cout<<endl;
}

void printFloatVector (vector<float> l) {
    vector<float>::iterator it;
    for (it = l.begin(); it != l.end(); it++) {
        cout<<(*it)<<" ";
    }
    cout<<endl;
}

int main () {
    
    // Declaration
    vector<float> first, second;
    
    // Initialisation
    vector<int> vectorFirst({10, 20, 15});
    
    // vectorSecond is intialised with 3 ints
    // having value as 45
    vector<int> vectorSecond(3, 45);
    
    cout<<"vectorFirst elements:"<<endl;
    printIntVector(vectorFirst);
    
    cout<<"vectorSecond elements:"<<endl;
    printIntVector(vectorSecond);
    
    int arr[3] = {100, 101, 102};
    vector<int> vectorThird;
    
    vectorThird.insert(vectorThird.begin(), arr, arr+3);
    
    cout<<"vectorThird elements after initialisation using arr:"<<endl;
    printIntVector(vectorThird);
    cout<<endl;
    
    
    cout<<"vectorFirst first element: "<<vectorFirst.front()<<endl;
    cout<<"vectorFirst last element: "<<vectorFirst.back()<<endl;
    
    
    vector<int>::iterator it;
    
    //Iterator to vector's first element
    it = vectorFirst.begin();
    //insert() returns pointer to the (new) first element
    it = vectorFirst.insert (it, 2);
    
    cout<<"vectorFirst elements after adding 2 at position (it):"<<endl;
    printIntVector(vectorFirst);
    
    //Iterator to 3rd element after vectorFirst.begin()
    vectorFirst.insert (it+3, 2, 300);
    
    cout<<"vectorFirst elements after adding 2 elements (value: 300) at position (it+3):"<<endl;
    printIntVector(vectorFirst);
    
    
    
    vectorFirst.swap(vectorSecond);
    
    cout<<"vectorFirst elements after swap:"<<endl;
    printIntVector(vectorFirst);
    cout<<"vectorSecond elements after swap:"<<endl;
    printIntVector(vectorSecond);
    
    vectorFirst.clear();
    cout<<"vectorFirst elements after clear:"<<endl;
    printIntVector(vectorFirst);

    if (vectorFirst.empty()) {
        cout<<"vectorFirst is empty"<<endl;
    }

    // push_back – adds a new element
    // at the end of the vector
    first.push_back (1.0);
    first.push_back (2.0);
    first.push_back (3.0);
    first.push_back (4.0);
    first.push_back (5.0);
    first.push_back (6.0);
    

    cout<<"first vector elements after push_back():"<<endl;
    printFloatVector(first);
    
    
    cout<<"first vector elements after pop_back():"<<endl;
    first.pop_back();
    printFloatVector(first);

    
    // erase – removes either a single element (position)
    // or a range of elements ([first,last))
    first.erase(first.begin() + 1, first.end() - 2);
    
    cout<<"first vector elements after removing the elements fromm 1 to 4"<<endl;
    printFloatVector(first);

    return 0;
}

Output

vectorFirst elements:
10 20 15 
vectorSecond elements:
45 45 45 
vectorThird elements after initialisation using arr:
100 101 102 

vectorFirst first element: 10
vectorFirst last element: 15
vectorFirst elements after adding 2 at position (it):
2 10 20 15 
vectorFirst elements after adding 2 elements (value: 300) at position (it+3):
2 10 20 300 300 15 
vectorFirst elements after swap:
45 45 45 
vectorSecond elements after swap:
2 10 20 300 300 15 
vectorFirst elements after clear:

vectorFirst is empty
first vector elements after push_back():
1 2 3 4 5 6 
first vector elements after pop_back():
1 2 3 4 5 
first vector elements after removing the elements from 1 to 2
1 4 5 

Here’s a working example:

https://ideone.com/2VKGaG

Leave a Reply

Your email address will not be published.