How to use the vector::size, vector::capacity, and vector::push_back STL functions in Visual C++

MORE INFORMATION

Required header

   <vector>

Prototypes

   size_type vector::capacity() const
   size_type vector::size() const
   void vector::push_back(const _TYPE& _X)

Description

• The sample declares an empty vector of integers.
• It outputs the size and capacity of the vector.
• It adds a single element to the vector, then outputs the size and capacity again.

Sample code

////////////////////////////////////////////////////////////////////// 
// 
// Compile options needed: /GX
// 
// Capacity.cpp  - Illustrates vector::capacity and vector::size
// 
// Functions:
// 
//    vector::capacity  - Return # of elements for which memory has
//                        been allocated.
// 
//    vector::size      - Return # of elements in the vector
// 
//    vector::push_back - Append (insert) an element to the end of a
//                        vector, allocating memory for it if necessary.
// 
// Written by Tom Campbell
// of Microsoft Corporation
// Copyright (c) 1996 Microsoft Corporation. All rights reserved.
////////////////////////////////////////////////////////////////////// 

// The debugger can't handle symbols more than 255 characters long.
// STL often creates symbols longer than that.
// This disables the warning issued when symbols are longer than 255 chars.
#pragma warning(disable:4786)

#include <iostream>
#include <vector>

#if _MSC_VER > 1020   // if VC++ version is > 4.2
   using namespace std;  // std c++ libs implemented in std
   #endif

typedef vector<int, allocator<int> > INTVECTOR;

void main()
{
    // Dynamically allocated vector begins with 0 elements.
    INTVECTOR theVector;

    // Show size (current # of elements) and capacity (# of elements
    // there's room for) of the empty vector.
    cout << endl << "Vector with no elements:" << endl;
    cout << "theVector's size is: " << theVector.size() << endl;
    cout << "theVector's capacity is: " << theVector.capacity() << endl;

    // Add one element to the end of the vector, an int with the value 42.
    // Allocate memory if necessary.
    theVector.push_back(42) ;

    // Show size & capacity after adding an element to the vector.
    cout << endl << "After adding 1 element:" << endl;
    cout << "theVector's size is: " << theVector.size() << endl;
    cout << "theVector's capacity is: " << theVector.capacity() << endl;
}