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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