C++ Tutorial/vector/vector elements

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Accessing Elements in a Vector Using Array Semantics

#include <iostream>
#include <vector>
using namespace std;
int main ()
{
    vector <int> v;
    // Insert sample integers into the vector:
    v.push_back (50);
    v.push_back (1);
    v.push_back (987);
    v.push_back (1001);
    unsigned int nElementIndex = 0;
    while (nElementIndex < v.size ()){
        cout << "Element at position " << nElementIndex;
        cout << " is: " << v [nElementIndex] << endl;
        ++ nElementIndex;
    }
    return 0;
}

Accessing Elements in a Vector Using Pointer Semantics (Iterators)

#include <iostream>
#include <vector>
int main ()
{
    using namespace std;
    vector <int> v;
    v.push_back (50);
    v.push_back (1);
    v.push_back (987);
    v.push_back (1001);
    // Access objects in a vector using iterators:
    vector<int>::iterator i = v.begin();
    while (i != v.end ())
    {
        size_t nElementIndex = distance (v.begin (),
                      i);
        cout << "Element at position ";
        cout << nElementIndex << " is: " << *i << endl;
        // move to the next element
        ++ i;
    }
    return 0;
}

Access the elements of a vector through an iterator.

#include <iostream>
#include <vector>
#include <cctype>
using namespace std;
   
int main()
{
  vector<char> v(10); // create a vector of length 10
  vector<char>::iterator p; // create an iterator
  int i;
   
  // assign elements in vector a value
  p = v.begin();
  i = 0;
  while(p != v.end()) {
    *p = i + "a";
    p++;
    i++;
  }
   
  // display contents of vector
  cout << "Original contents:\n";
  p = v.begin();
  while(p != v.end()) {
    cout << *p << " ";
    p++;
  }
  cout << "\n\n";
   
  // change contents of vector
  p = v.begin();
  while(p != v.end()) {
    *p = toupper(*p);
    p++;
  }
   
  // display contents of vector
  cout << "Modified Contents:\n";
  p = v.begin();
  while(p != v.end()) {
    cout << *p << " ";
    p++;
  }
  cout << endl;
   
  return 0;
}

Add all the elements from vector Two to the end of vector One

#include <vector>
#include <algorithm>
#include <iterator>
#include <iostream>
using namespace std;
void printVector(const vector<int>& v){
  copy(v.begin(), v.end(), ostream_iterator<int>(cout, " "));
  cout << endl;
}
int main(int argc, char** argv){
  vector<int> v1, v2;
  int i;
  v1.push_back(1);
  v1.push_back(2);
  v1.push_back(3);
  v1.push_back(5);
  // Insert it in the correct place
  v1.insert(v1.begin() + 3, 4);
  // Add elements 6 through 10 to v2
  for (i = 6; i <= 10; i++) {
    v2.push_back(i);
  }
  printVector(v1);
  printVector(v2);
  // add all the elements from v2 to the end of v1
  v1.insert(v1.end(), v2.begin(), v2.end());
  printVector(v1);
  return (0);
}

Add elements to the end of vector with push_back

#include <iostream>
#include <vector>
using namespace std;
void show(const char *msg, vector<int> vect);
int main() {
  // Declare a vector that has an initial capacity of 10.
  vector<int> v(10);
  for(unsigned i=0; i < v.size(); ++i) v[i] = i*i;
  show("Contents of v: ", v);
  // Add elements to the end of v.
  v.push_back(100);
  v.push_back(121);

  return 0;
}
// Display the contents of a vector<int>.
void show(const char *msg, vector<int> vect) {
  cout << msg;
  for(unsigned i=0; i < vect.size(); ++i)
    cout << vect[i] << " ";
  cout << "\n";
}

append one more element. This causes reallocation

#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;
template <class T>
void print(T& c){
   for( typename T::iterator i = c.begin(); i != c.end(); i++ ){
      std::cout << *i << endl;
   }
}
int main( )
{
   vector<double> v( 5, 2.78 );
   v[2] = 0.0;
   // make the vector as large as possible without reallocating
   v.resize( v.capacity(), 2.78 );
   // find the smallest number
   vector<double>::iterator before_itr = min_element( v.begin(), v.end() );
   // append one more element. This causes reallocation
   v.push_back( 2.78 );
}

Change element with const iterator

#include <vector> 
#include <iostream> 
using namespace std; 
vector<double> makevector(int size){
  vector<double> result;
  for (int i=1; i<=size; i++) { 
    result.push_back(double(i)); 
  } 
  return result; 
} 
void print(const vector<double>& l) 
{ 
  cout << "Size of vector is: " << l.size() << endl; 
  vector<double>::const_iterator i; 
  for (i=l.begin(); i!=l.end(); i++) 
  { 
    cout << (*i) << " "; 
  } 
  cout << endl; 
} 
int main() 
{ 
  vector<double> vector1=makevector(5); 
  vector<double>::iterator bi; 
  vector<double>::reverse_iterator ri; 
  ri=vector1.rbegin();          // Set iterator 
  while (ri!=vector1.rend()) cout << (*ri++) << " "; 
  cout << endl << endl; 
  // Change element with const iterator 
  cout << "Change first element with const iterator" << endl; 
  vector<double>::const_iterator ci; 
  ci=vector1.end(); 
  ci--; 
  cout << *ci << endl; 
}

Change element with pointer

#include <vector> 
#include <iostream> 
using namespace std; 
vector<double> makevector(int size){
  vector<double> result;
  for (int i=1; i<=size; i++) { 
    result.push_back(double(i)); 
  } 
  return result; 
} 
void print(const vector<double>& l) 
{ 
  cout << "Size of vector is: " << l.size() << endl; 
  vector<double>::const_iterator i; 
  for (i=l.begin(); i!=l.end(); i++) 
  { 
    cout << (*i) << " "; 
  } 
  cout << endl; 
} 
int main() 
{ 
  vector<double> vector1=makevector(5); 
  vector<double>::iterator bi; 
  vector<double>::reverse_iterator ri; 
  ri=vector1.rbegin();          // Set iterator 
  while (ri!=vector1.rend()) cout << (*ri++) << " "; 
  cout << endl << endl; 
  // Change element 
  cout << "Change first element with mutable iterator" << endl; 
  bi=vector1.begin(); 
  *bi=double(99); 
  print(vector1); 
}

Constructing a Container That Has Identical Elements

#include <vector>
#include <iostream>
using namespace std;
template <class T>
void print(T& c){
   for( typename T::iterator i = c.begin(); i != c.end(); i++ ){
      std::cout << *i << endl;
   }
}

int main( )
{
   const int num_elements = 5;
   const float value = 3.14f;
   // construct a vector filled with copies of one value
   vector<float> v( num_elements, value );
   print( v);
}

Constructing a Container That Has Specified Values

#include <list>
#include <vector>
#include <iostream>
using namespace std;
template <class T>
void print(T& c){
   for( typename T::iterator i = c.begin(); i != c.end(); i++ ){
      std::cout << *i << endl;
   }
}
int main( )
{
   const int num_elements = 4;
   const double data[num_elements] = { 4.78, 6.97, 8.81, 9.02 };
   list<double> l( data, data + num_elements );
   const char* flavors[] = { "A", "B", "C" };
   vector<string> v( flavors,
      flavors + sizeof( flavors ) / sizeof( flavors[0] ) );
   // display containers
   print( l );
   print( v );
}

Elements Being Created, Assigned, and Destroyed

#include <iostream>
#include <vector>
using namespace std;
class Element
{
   public:
   Element();
   Element( const Element& );
   ~Element();
   Element& operator=( const Element& );
};
inline
Element::Element()
{ cout << "\nIn default constructor"; }
inline
Element::Element( const Element& )
{ cout << "\nIn copy constructor"; }
inline
Element::~Element()
{ cout << "\nIn destructor"; }
inline
Element& Element::operator=( const Element& )
{
   cout << "\nIn assignment operator";
   return *this;
}
int main( )
{
   cout << "Constructing Vector With Three Elements";
   vector<Element> d( 3 );
   cout << "\n\nDeleting First Element";
   d.erase( d.begin() );
   cout << "\n\nDeleting All Elements";
   d.clear();
}

Instantiate a vector to 5 elements taken from another

#include <vector>
int main ()
{
   std::vector <int> v;
   // Instantiate a vector with 10 elements (it can grow larger)
   std::vector <int> v1 (10);
   // Instantiate a vector with 10 elements, each initialized to 90
   std::vector <int> vecArrayWithTenInitializedElements (10, 90);
   // Instantiate one vector and initialize it to the contents of another
   std::vector <int> vecArrayCopy (vecArrayWithTenInitializedElements);
   // Instantiate a vector to 5 elements taken from another
   std::vector<int> vecSomeElementsCopied(v.begin(), v.begin () + 5);
   return 0;
}

Instantiate a vector with 10 elements, each initialized to 90

#include <vector>
int main ()
{
   std::vector <int> v;
   // Instantiate a vector with 10 elements (it can grow larger)
   std::vector <int> v1 (10);
   // Instantiate a vector with 10 elements, each initialized to 90
   std::vector <int> vecArrayWithTenInitializedElements (10, 90);
   return 0;
}

Instantiate a vector with 10 elements (it can grow larger)

#include <vector>
int main ()
{
   std::vector <int> v;
   // Instantiate a vector with 10 elements (it can grow larger)
   std::vector <int> v1 (10);

   return 0;
}

Instantiate a vector with 4 elements, each initialized to 90

#include <vector>
#include <iostream>
int main ()
{
    using namespace std;
    // Instantiate a vector with 4 elements, each initialized to 90
    vector <int> v (4, 90);
    vector <int>::iterator i;
    for ( i = v.begin (); i != v.end (); ++ i ){
        cout << *i << " ";
    }
    return 0;
}

Set Element Values in a vector Using Array Semantics

#include <vector>
#include <iostream>
int main ()
{
    std::vector <int> v (4);
    // Copy integer values into individual element locations
    v [0] = 50;
    v [1] = 1;
    v [2] = 987;
    v [3] = 1001;
    std::cout << "The vector contains ";
    std::cout << v.size () << " Elements";
    return 0;
}

The first and last element in vector as pointed to by begin() and end() - 1

#include <iostream>
#include <vector>
using namespace std;
void show(const char *msg, vector<int> vect);
int main() {
  // Declare a vector that has an initial capacity of 10.
  vector<int> v(10);
  for(unsigned i=0; i < v.size(); ++i) v[i] = i*i;
  show("Contents of v: ", v);
  // the use of the subscripting operator.
  int sum = 0;
  for(unsigned i=0; i < v.size(); ++i) sum += v[i];
  double avg = sum / v.size();
  cout << "The average of the elements is " << avg << "\n\n";
  // Add elements to the end of v.
  v.push_back(100);
  v.push_back(121);
  show("v after pushing elements onto the end: ", v);
  cout << endl;
  // Now use pop_back() to remove one element.
  v.pop_back();
  show("v after back-popping one element: ", v);
  cout << endl;
  cout << "The first and last element in v as"
       << " pointed to by begin() and end()-1:\n"
       << *v.begin() << ", " << *(v.end()-1) << "\n\n";
  return 0;
}
void show(const char *msg, vector<int> vect) {
  cout << msg << endl;
  for(unsigned i=0; i < vect.size(); ++i)
    cout << vect[i] << endl;
}

The first and last element in vector as pointed to by rbegin() and rend() - 1

#include <iostream>
#include <vector>
using namespace std;
void show(const char *msg, vector<int> vect);
int main() {
  // Declare a vector that has an initial capacity of 10.
  vector<int> v(10);
  for(unsigned i=0; i < v.size(); ++i) v[i] = i*i;
  show("Contents of v: ", v);
  // the use of the subscripting operator.
  int sum = 0;
  for(unsigned i=0; i < v.size(); ++i) sum += v[i];
  double avg = sum / v.size();
  cout << "The average of the elements is " << avg << "\n\n";
  // Add elements to the end of v.
  v.push_back(100);
  v.push_back(121);
  cout << "The first and last element in v as"
       << " pointed to by rbegin() and rend()-1:\n"
       << *v.rbegin() << ", " << *(v.rend()-1) << "\n\n";
  return 0;
}
void show(const char *msg, vector<int> vect) {
  cout << msg << endl;
  for(unsigned i=0; i < vect.size(); ++i)
    cout << vect[i] << endl;
}

Vector Creation and Element Access

#include <iostream>
 #include <string>
 #include <vector>
 using namespace std;
 class Employee
 {
 public:
        Employee();
        Employee(const string& name, const int age);
        Employee(const Employee& rhs);
        ~Employee();
  
        void    SetName(const string& name);
        string  GetName()      const;
        void    SetAge(const int age);
        int     GetAge()       const;
        Employee& operator=(const Employee& rhs);
 
private:
        string itsName;
        int itsAge;
};
Employee::Employee()
: itsName("New Employee"), itsAge(16)
{}
Employee::Employee(const string& name, const int age)
: itsName(name), itsAge(age)
{}
Employee::Employee(const Employee& rhs)
: itsName(rhs.GetName()), itsAge(rhs.GetAge())
{}
Employee::~Employee()
{}
 
void Employee::SetName(const string& name)
{
        itsName = name;
}
string Employee::GetName() const
{
        return itsName;
}
void Employee::SetAge(const int age)
{
        itsAge = age;
}
int Employee::GetAge() const
{
        return itsAge;
}
Employee& Employee::operator=(const Employee& rhs)
{
        itsName = rhs.GetName();
        itsAge = rhs.GetAge();
        return *this;
}
ostream& operator<<(ostream& os, const Employee& rhs)
{
        os << rhs.GetName() << " is " << rhs.GetAge()  << " years old";
        return os;
}
template<class T>
void ShowVector(const vector<T>& v);    // display vector properties
typedef vector<Employee>        SchoolClass;
int main()
{
        Employee Harry;
        Employee Sally("Sally", 15);
        Employee Bill("Bill", 17);
        Employee Peter("Peter", 16);
        SchoolClass    EmptyClass;
        cout << "EmptyClass:\n";
        ShowVector(EmptyClass);
        SchoolClass GrowingClass(3);
        cout << "GrowingClass(3):\n";
        ShowVector(GrowingClass);
        GrowingClass[0] = Harry;
        GrowingClass[1] = Sally;
        GrowingClass[2] = Bill;
        cout << "GrowingClass(3) after assigning students:\n";
        ShowVector(GrowingClass);
        GrowingClass.push_back(Peter);
        cout << "GrowingClass() after added 4th student:\n";
        ShowVector(GrowingClass);
 
        GrowingClass[0].SetName("Harry");
        GrowingClass[0].SetAge(18);
        cout << "GrowingClass() after Set\n:";
        ShowVector(GrowingClass);
         
        return 0;
}
template<class T>
void ShowVector(const vector<T>& v)
{
        cout << "max_size() = " << v.max_size();
        cout << "\tsize() = " << v.size();
        cout << "\tcapacity() = " << v.capacity();
        cout << "\t" << (v.empty()? "empty": "not empty");
        cout << "\n";
 
        for (int i = 0; i < v.size(); ++i)
                cout << v[i] << "\n";
 
        cout << endl;
 }
Источник — «http://cppe.ru/index.php?title=C%2B%2B_Tutorial/vector/vector_elements&oldid=2221»