C++ vectors do a lot under the hood.

1VectorTest.cpp

#include <vector>
#include <cstdio>
using namespace std;

class Test
{
public:
	Test()
	{
		printf("  Test being created!\n");
	}

	~Test()
	{
		printf("  Test being destroyed!\n");
	}

	Test(const Test& copy)
	{
		printf("  Test being copied!\n");
	}
};

int main(int argc, char **argv)
{
	vector<Test> testVector;

	printf("Reserving room for 10 test objects.\n");
	testVector.reserve(10);

	printf("Resizing the vector to 10 objects.\n");
	testVector.resize(10);

	printf("Clearing the vector.\n");
	testVector.clear();

	printf("Resizing the vector back down to 1 object.\n");
	testVector.resize(1);

	printf("Adding 10 test objects\n");
	for (int i = 0;i < 10; i++) {
		testVector.push_back(Test());
	}

	printf("Clearing the vector.\n");
	testVector.clear();

	printf("Resizing the vector back down to 1 object.\n");
	testVector.resize(1);

	printf("Reserving room for 10 objects and adding them.\n");
	testVector.reserve(10);
	for (int i = 0;i < 10; i++) {
		testVector.push_back(Test());
	}

	printf("Leaving main()\n");
	return 0;
}

2Output.txt

./vtest 
Reserving room for 10 test objects.
Resizing the vector to 10 objects.
  Test being created!
  Test being copied!
  Test being copied!
  Test being copied!
  Test being copied!
  Test being copied!
  Test being copied!
  Test being copied!
  Test being copied!
  Test being copied!
  Test being copied!
  Test being copied!
  Test being destroyed!
  Test being destroyed!
Clearing the vector.
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
Resizing the vector back down to 1 object.
  Test being created!
  Test being copied!
  Test being copied!
  Test being destroyed!
  Test being destroyed!
Adding 10 test objects
  Test being created!
  Test being copied!
  Test being destroyed!
  Test being created!
  Test being copied!
  Test being destroyed!
  Test being created!
  Test being copied!
  Test being destroyed!
  Test being created!
  Test being copied!
  Test being destroyed!
  Test being created!
  Test being copied!
  Test being destroyed!
  Test being created!
  Test being copied!
  Test being destroyed!
  Test being created!
  Test being copied!
  Test being destroyed!
  Test being created!
  Test being copied!
  Test being destroyed!
  Test being created!
  Test being copied!
  Test being destroyed!
  Test being created!
  Test being copied!
  Test being copied!
  Test being copied!
  Test being copied!
  Test being copied!
  Test being copied!
  Test being copied!
  Test being copied!
  Test being copied!
  Test being copied!
  Test being copied!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
Clearing the vector.
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
Resizing the vector back down to 1 object.
  Test being created!
  Test being copied!
  Test being copied!
  Test being destroyed!
  Test being destroyed!
Reserving room for 10 objects and adding them.
  Test being created!
  Test being copied!
  Test being destroyed!
  Test being created!
  Test being copied!
  Test being destroyed!
  Test being created!
  Test being copied!
  Test being destroyed!
  Test being created!
  Test being copied!
  Test being destroyed!
  Test being created!
  Test being copied!
  Test being destroyed!
  Test being created!
  Test being copied!
  Test being destroyed!
  Test being created!
  Test being copied!
  Test being destroyed!
  Test being created!
  Test being copied!
  Test being destroyed!
  Test being created!
  Test being copied!
  Test being destroyed!
  Test being created!
  Test being copied!
  Test being destroyed!
Leaving main()
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!
  Test being destroyed!