In initialize vector c++, A vector is a dynamic array class executed in the default C++ library. It vector class has the capacity to dynamically expand with reduce. The component are placed in a adjacent rage therefor that they can be traversed by iterators.
The very first step imp in using vectors is to know how to declare as well as initialize them; there are 5+ several ways of initializing a vector in C++ Examples:
initialize vector c++
Also You can learn std::vector in C++, What is std::vector?, Declaration of std::vector, Initialization of std::vector, Length of std::vector, Passing std::vector to function, Multidimensional std::vector, Passing a multidimensional std::vector to a function or many more Member Functions.
There are the following the Initialize a define vector in C++ as shown below:(5 several ways)
Initialization vector can be done in several ways with examples of vectors
- Initializing by pushing values one by one
- Specifying size and initializing all values
- Initializing like arrays
- Initializing from an array
- Initializing from another vector
vector c++ & c++ vector initialization
Creating a vector object without any types of the initialization will make an empty vector with no any elements example like.
std::vector<int> vecOfInts;
Initializing by pushing values one by one :
// c++ Example to make an empty vector
// with push values step by step.
#include <bits/stdc++.h>
using namespace std;
int main()
{
// Make an empty vector
vector<int> myvct;
myvct.push_back(40);
myvct.push_back(50);
myvct.push_back(60);
for (int x : myvct)
cout << x << " ";
return 0;
}
Specifying size and initializing all values :
// c++ Example to make an empty vector
// with push values step by step.
#include <bits/stdc++.h>
using namespace std;
int main()
{
int n = 3;
// Create a vector of size n with
// all values as 40.
vector<int> myvct(n, 40);
for (int x : myvct)
cout << x << " ";
return 0;
}
Initializing like arrays :
// c++ Example to initialize a vector like
// an array.
#include <bits/stdc++.h>
using namespace std;
int main()
{
vector<int> myvct{ 40, 50, 60 };
for (int x : myvct)
cout << x << " ";
return 0;
}
Initializing from an array :
// c++ Example to initialize a vector from
// an array.
#include <bits/stdc++.h>
using namespace std;
int main()
{
int arr[] = { 40, 50, 60 };
int n = sizeof(arr) / sizeof(arr[0]);
vector<int> myvct(arr, arr + n);
for (int x : myvct)
cout << x << " ";
return 0;
}
Initializing from another vector :
// c++ Example to initialize a vector from
// second vector.
#include <bits/stdc++.h>
using namespace std;
int main()
{
vector<int> myvct1{ 40, 50, 60 };
vector<int> myvct2(myvct1.begin(), myvct1.end());
for (int x : myvct2)
cout << x << " ";
return 0;
}
std::vector in C++
Length of std::vector
#include <iostream>
#include <vector>
int main()
{
std::vector<int> ages = {41, 98, 27, 14, 58};
ages = {45, 35, 15};
std::cout << "length of array : " << ages.size() << std::endl;
return 0;
}
Passing std::vector to function
#include <iostream>
#include <vector>
using namespace std;
void printVector(const std::vector<int> &n)
{
for (int j = 0; j < n.size(); j++ )
{
cout << "n[" << j << "] = " << n[j] << endl;
}
}
int main()
{
vector<int> n = {1,2,3,4,5};
printVector(n);
return 0;
}
Member Functions
There are the following the Member Functions several ways Like as front, back, empty, resize, max_size, assign, push_back, pop_back, capacity, reserve, insert, erase, clear, c++ push_back, vector push_back, push_back c++ and swap.
at
#include <iostream>
#include <vector>
using namespace std;
int main()
{
vector<int> ages = {41, 98, 27, 14, 58};
ages.at(2) = 72;
for(int i = 0; i < ages.size() ; i++)
{
cout << "ages[" << i << "] = " << ages.at(i) << endl;
}
return 0;
}
front
#include <iostream>
#include <vector>
using namespace std;
int main()
{
vector<int> ages = {41, 98, 27, 14, 58};
cout << ages.front() << endl;
return 0;
}
back
#include <iostream>
#include <vector>
using namespace std;
int main()
{
vector<int> ages = {41, 98, 27, 14, 58};
cout << ages.back() << endl;
return 0;
}
empty
#include <iostream>
#include <vector>
using namespace std;
int main()
{
vector<int> myvct1 = {5, 6};
vector<int> myvct2;
cout << myvct1.empty() << endl;
cout << myvct2.empty() << endl;
return 0;
}
resize
#include <iostream>
#include <vector>
using namespace std;
int main()
{
vector<int> myvct1 = {5, 6};
myvct1.resize(5);
for(int i = 0; i < myvct1.size() ; i++)
{
cout << myvct1[i] << endl;
}
return 0;
}
max_size
#include <iostream>
#include <vector>
using namespace std;
int main()
{
vector<int> myvct1 = {11, 12, 13, 14, 15};
cout << myvct1.size() << endl;
cout << myvct1.max_size() << endl;
return 0;
}
assign
#include <iostream>
#include <vector>
using namespace std;
int main()
{
vector<int> myvct;
myvct.assign(7, 40); // 7 elements each of value 40
cout << myvct.size() << endl;
return 0;
}
push_back
#include <iostream>
#include <vector>
using namespace std;
int main()
{
vector<int> myvct = {14, 15, 16, 17, 18};
myvct.push_back(47);
//printing values of myvct
cout << "elements of myvct" << endl;
for(int i = 0; i < myvct.size(); i++)
{
cout << myvct[i] << endl;
}
return 0;
}
pop_back
#include <iostream>
#include <vector>
using namespace std;
int main()
{
vector<int> myvct = {14, 15, 16, 17, 18};
myvct.pop_back();
//printing values of myvct
cout << "elements of myvct" << endl;
for(int i = 0; i < myvct.size(); i++)
{
cout << myvct[i] << endl;
}
return 0;
}
capacity
#include <iostream>
#include <vector>
using namespace std;
int main()
{
vector<int> myvct1;
for(int i = 0; i < 50; i++)
{
myvct1.push_back(1);
}
cout << "size : " << myvct1.size() << endl;
cout << "max_size : " << myvct1.max_size() << endl;
cout << "capacity : " << myvct1.capacity() << endl;
return 0;
}
reserve
#include <iostream>
#include <vector>
using namespace std;
int main()
{
vector<int> myvct1;
for(int i = 0; i < 50; i++)
{
myvct1.push_back(1);
}
myvct1.reserve(100);
cout << "capacity : " << myvct1.capacity() << endl;
return 0;
}
insert
#include <iostream>
#include <vector>
#include <iterator>
using namespace std;
void printVector(const std::vector<int> &n)
{
cout << "Vector is :" << endl;
for (auto i: n)
{
std::cout << ' ' << i;
}
std::cout << '\n';
}
int main()
{
vector<int> myvct = {111,222};
printVector(myvct);
auto it = myvct.begin();
myvct.insert(it,000);
printVector(myvct);
it = myvct.begin();
myvct.insert(it,3,333);
printVector(myvct);
vector<int> myvct1 = {555,555};
it = myvct.begin();
myvct.insert(it+4, myvct1.begin(), myvct1.end());
printVector(myvct);
return 0;
}
erase
#include <iostream>
#include <vector>
#include <iterator>
using namespace std;
int main()
{
vector<int> myvct1 = {14, 15, 16, 17, 18};
vector<int> myvct2 = {11, 12, 13, 14, 15};
myvct1.erase(myvct1.begin()+4); // removing a single element at position 4
myvct2.erase(myvct2.begin()+1, myvct2.begin()+3); // removing range of elements from position 1 till 2
//printing the values of myvct1
cout << "Values of myvct1" << endl;
for(int i = 0; i < myvct1.size(); i++)
{
cout << myvct1[i] << endl;
}
//printing the values of myvct2
cout << "Values of myvct2" << endl;
for(int i = 0; i < myvct2.size(); i++)
{
cout << myvct2[i] << endl;
}
return 0;
}
clear
#include <iostream>
#include <vector>
using namespace std;
int main()
{
vector<int> myvct1 = {14, 15, 16, 17, 18};
myvct1.clear();
for (auto i: myvct1)
{
std::cout << i << endl;
}
return 0;
}
swap
#include <iostream>
#include <vector>
using namespace std;
int main()
{
vector<int> myvct1 = {1, 2, 3};
vector<int> myvct2 = {4, 5, 6};
myvct1.swap(myvct2);
std::cout << "Vector myvct1" << endl;
for (auto i: myvct1)
{
std::cout << i << endl;
}
std::cout << "Vector myvct2" << endl;
for (auto i: myvct2)
{
std::cout << i << endl;
}
return 0;
}
Multidimensional std::vector
#include <iostream>
#include <vector>
using namespace std;
int main()
{
vector<vector<int>> v {{{1,2,3},{4,5,6},{7,8,9}}};
for(int i=0; i<3; i++)
{
for(int j=0; j<3; j++)
{
cout << v[i][j] << "\t";
}
cout << endl;
}
return 0;
}
Passing a multidimensional std::vector to a function
#include <iostream>
#include <vector>
using namespace std;
void display(const std::vector<std::vector<int>> &v)
{
for(int i=0; i<v.size(); i++)
{
for(int j = 0; j<v[i].size(); j++)
{
cout << v[i][j] << "\t";
}
cout << endl;
}
}
int main()
{
vector<vector<int>> v {{{1,2,3},{4,5,6},{7,8,9}}};
display(v);
return 0;
}
See also
| vector::operator= | Assign content (public member function) |
| vector::assign | Assign vector content (public member function) |
| vector::reserve | Request a change in capacity (public member function) |
| vector::resize | Change size (public member function) |
| vector::clear | Clear content (public member function) |
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