Question

How push_back() increase size and capacity of a vector in C++

Answer 1

#include <iostream>
#include <vector>
#include <algorithm>

using std::cout;
using std::endl;
using std::vector;

int main()
{
	vector<char> vec(10);

	cout << "size: " << vec.size() << endl;
	cout << "capacity: " << vec.capacity() << endl;

	vec.push_back('z');

	cout << endl << "push_back" << endl << endl;

	cout << "size: " << vec.size() << endl;
	cout << "capacity: " << vec.capacity() << endl;
	
	return 0;
}

/*
run:

size: 10
capacity: 10

push_back

size: 11
capacity: 15

*/

 

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Answer 2

#include <iostream>
#include <vector>
#include <algorithm>

using std::cout;
using std::endl;
using std::vector;

int main()
{
	vector<char> vec(10);

	vec.resize(100);

	cout << "size: " << vec.size() << endl;
	cout << "capacity: " << vec.capacity() << endl;

	vec.push_back('z');

	cout << endl << "push_back" << endl << endl;

	cout << "size: " << vec.size() << endl;
	cout << "capacity: " << vec.capacity() << endl;
	
	return 0;
}

/*
run:

size: 100
capacity: 100

push_back

size: 101
capacity: 150

*/

 

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