C++ Tutorial/STL Algorithms Non modifying sequence operations/for each

Call custom function in for_each

<source lang="cpp">/* The following code example is taken from the book

* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/

1. include <iostream>
2. include <vector>
3. include <deque>
4. include <list>
5. include <set>
6. include <map>
7. include <string>
8. include <algorithm>
9. include <iterator>
10. include <functional>
11. include <numeric>

/* PRINT_ELEMENTS()

* - prints optional C-string optcstr followed by
* - all elements of the collection coll
* - separated by spaces
*/

template <class T> inline void PRINT_ELEMENTS (const T& coll, const char* optcstr="") {

   typename T::const_iterator pos;
   std::cout << optcstr;
   for (pos=coll.begin(); pos!=coll.end(); ++pos) {
       std::cout << *pos << " ";
   }
   std::cout << std::endl;

} /* INSERT_ELEMENTS (collection, first, last)

* - fill values from first to last into the collection
* - NOTE: NO half-open range
*/

template <class T> inline void INSERT_ELEMENTS (T& coll, int first, int last) {

   for (int i=first; i<=last; ++i) {
       coll.insert(coll.end(),i);
   }

} using namespace std; // function object that adds the value with which it is initialized template <class T> class AddValue {

 private:
   T theValue;    // value to add
 public:
   // constructor initializes the value to add
   AddValue (const T& v) : theValue(v) {
   }
   // the function call for the element adds the value
   void operator() (T& elem) const {
       elem += theValue;
   }

}; int main() {

   vector<int> coll;
   INSERT_ELEMENTS(coll,1,9);
   // add ten to each element
   for_each (coll.begin(), coll.end(),       // range
             AddValue<int>(10));             // operation
   PRINT_ELEMENTS(coll);
   // add value of first element to each element
   for_each (coll.begin(), coll.end(),       // range
             AddValue<int>(*coll.begin()));  // operation
   PRINT_ELEMENTS(coll);

}</source>

11 12 13 14 15 16 17 18 19
22 23 24 25 26 27 28 29 30

The square of every integer in a vector

<source lang="cpp">#include <iostream>

1. include <algorithm>
2. include <numeric>
3. include <vector>

using namespace std; void outputSquare( int ); int main(){

  const int SIZE = 10;
  int a1[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
  vector< int > v( a1, a1 + SIZE );
  random_shuffle( v.begin(), v.end() );

  cout << "\n\nThe square of every integer in Vector v is:\n";
  for_each( v.begin(), v.end(), outputSquare );
  cout << endl;
  return 0;

} void outputSquare( int value ) { cout << value * value << " "; }</source>

Use custom function and for_each to calculate mean value

<source lang="cpp">/* The following code example is taken from the book

* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/

1. include <iostream>
2. include <vector>
3. include <deque>
4. include <list>
5. include <set>
6. include <map>
7. include <string>
8. include <algorithm>
9. include <iterator>
10. include <functional>
11. include <numeric>

/* PRINT_ELEMENTS()

* - prints optional C-string optcstr followed by
* - all elements of the collection coll
* - separated by spaces
*/

template <class T> inline void PRINT_ELEMENTS (const T& coll, const char* optcstr="") {

   typename T::const_iterator pos;
   std::cout << optcstr;
   for (pos=coll.begin(); pos!=coll.end(); ++pos) {
       std::cout << *pos << " ";
   }
   std::cout << std::endl;

} /* INSERT_ELEMENTS (collection, first, last)

* - fill values from first to last into the collection
* - NOTE: NO half-open range
*/

template <class T> inline void INSERT_ELEMENTS (T& coll, int first, int last) {

   for (int i=first; i<=last; ++i) {
       coll.insert(coll.end(),i);
   }

} using namespace std; // function object to process the mean value class MeanValue {

 private:
   long num;    // number of elements
   long sum;    // sum of all element values
 public:
   // constructor
   MeanValue () : num(0), sum(0) {
   }
   // function call
   // - process one more element of the sequence
   void operator() (int elem) {
       num++;          // increment count
       sum += elem;    // add value
   }
   // return mean value (implicit type conversion)
   operator double() {
       return static_cast<double>(sum) / static_cast<double>(num);
   }

}; int main() {

   vector<int> coll;
   INSERT_ELEMENTS(coll,1,8);
   // process and print mean value
   double mv = for_each (coll.begin(), coll.end(),  // range
                         MeanValue());              // operation
   cout << "mean value: " << mv << endl;

}</source>

mean value: 4.5

Use for_each() algorithm to show elements in a vector and do the summation

<source lang="cpp">#include <iostream>

1. include <vector>
2. include <algorithm>

using namespace std; void show(int i) {

 cout << i << endl;

} // A running sum. int summation(int i) {

 static int sum = 0;
 sum += i;
 return sum;

} int main() {

 vector<int> v;
 int i;
 for(i=1; i < 11; i++) v.push_back(i);
 for_each(v.begin(), v.end(), show);
 for_each(v.begin(), v.end(), summation);
 
 cout << summation(0);
 return 0;

}</source>

Use for_each function to add first element to each element in the list

<source lang="cpp">/* The following code example is taken from the book

* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/

1. include <iostream>
2. include <list>
3. include <algorithm>

using namespace std; /* PRINT_ELEMENTS()

* - prints optional C-string optcstr followed by
* - all elements of the collection coll
* - separated by spaces
*/

template <class T> inline void PRINT_ELEMENTS (const T& coll, const char* optcstr="") {

   typename T::const_iterator pos;
   std::cout << optcstr;
   for (pos=coll.begin(); pos!=coll.end(); ++pos) {
       std::cout << *pos << " ";
   }
   std::cout << std::endl;

}

// function object that adds the value with which it is initialized class AddValue {

 private:
   int theValue;    // the value to add
 public:
   // constructor initializes the value to add
   AddValue(int v) : theValue(v) {
   }
   // the ""function call"" for the element adds the value
   void operator() (int& elem) const {
       elem += theValue;
   }

}; int main() {

   list<int> coll;
   // insert elements from 1 to 9
   for (int i=1; i<=9; ++i) {
       coll.push_back(i);
   }
   PRINT_ELEMENTS(coll,"initialized:                ");
   // add value of first element to each element
   for_each (coll.begin(), coll.end(),    // range
             AddValue(*coll.begin()));    // operation
   PRINT_ELEMENTS(coll,"after adding first element: ");

}</source>

initialized:                1 2 3 4 5 6 7 8 9
after adding first element: 2 3 4 5 6 7 8 9 10

Use for_each function to add value for each element

<source lang="cpp">/* The following code example is taken from the book

* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/

1. include <iostream>
2. include <list>
3. include <algorithm>

using namespace std; /* PRINT_ELEMENTS()

* - prints optional C-string optcstr followed by
* - all elements of the collection coll
* - separated by spaces
*/

template <class T> inline void PRINT_ELEMENTS (const T& coll, const char* optcstr="") {

   typename T::const_iterator pos;
   std::cout << optcstr;
   for (pos=coll.begin(); pos!=coll.end(); ++pos) {
       std::cout << *pos << " ";
   }
   std::cout << std::endl;

}

// function object that adds the value with which it is initialized class AddValue {

 private:
   int theValue;    // the value to add
 public:
   // constructor initializes the value to add
   AddValue(int v) : theValue(v) {
   }
   // the ""function call"" for the element adds the value
   void operator() (int& elem) const {
       elem += theValue;
   }

}; int main() {

   list<int> coll;
   // insert elements from 1 to 9
   for (int i=1; i<=9; ++i) {
       coll.push_back(i);
   }
   PRINT_ELEMENTS(coll,"initialized:                ");
   // add value 10 to each element
   for_each (coll.begin(), coll.end(),    // range
             AddValue(10));               // operation
   PRINT_ELEMENTS(coll,"after adding 10:            ");

}</source>

initialized:                1 2 3 4 5 6 7 8 9
after adding 10:            11 12 13 14 15 16 17 18 19

Use for_each function to print all elements in a vector

<source lang="cpp">/* The following code example is taken from the book

* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/

1. include <iostream>
2. include <vector>
3. include <algorithm>

using namespace std; // function that prints the passed argument void print (int elem) {

   cout << elem << " ";

} int main() {

   vector<int> coll;
   // insert elements from 1 to 9
   for (int i=1; i<=9; ++i) {
       coll.push_back(i);
   }
   // print all elements
   for_each (coll.begin(), coll.end(),    // range
             print);                      // operation
   cout << endl;

}</source>

1 2 3 4 5 6 7 8 9

Use for_each with predicate

<source lang="cpp">#include <iostream> using std::cout; using std::endl;

1. include <algorithm>
2. include <numeric>
3. include <vector>
4. include <iterator>

void outputSquare( int ); int main() {

 std::ostream_iterator< int > output( cout, " " );
  int a2[ 10 ] = { 100, 2, 8, 1, 50, 3, 8, 8, 9, 10 };
  std::vector< int > v2( a2, a2 + 10 ); // copy of a2
  cout << "Vector v2 contains: ";
  std::copy( v2.begin(), v2.end(), output );
  // output square of every element in v
  cout << "\n\nThe square of every integer in Vector v is:\n";
  std::for_each( v2.begin(), v2.end(), outputSquare );
  cout << endl;
  return 0;

} void outputSquare( int value ) {

  cout << value * value << " ";

}</source>

Vector v2 contains: 100 2 8 1 50 3 8 8 9 10
The square of every integer in Vector v is:
10000 4 64 1 2500 9 64 64 81 100

Using for_each to Display the Contents of a Collection

<source lang="cpp">#include <algorithm>

1. include <iostream>
2. include <vector>
3. include <string>

using namespace std; template <typename elementType> class DisplayCounter{ private:

   int m_nCount;

public:

   DisplayCounter (){
       m_nCount = 0;
   }
   void operator () (const elementType& element) {
       ++ m_nCount;
       cout << element << " ";
   }
   int GetCount(){
       return m_nCount;
   }

}; int main (){

   vector <int> v;
   for (int nCount = 0; nCount < 10; ++ nCount)
       v.push_back (nCount);
   DisplayCounter<int> mIntResult = for_each ( v.begin (), v.end(), DisplayCounter<int> () );
   cout << mIntResult.GetCount () << endl;

   string str ("this is a test");
   cout << str << endl << endl;
   DisplayCounter<char> mCharResult = for_each (str.begin(), str.end(),DisplayCounter<char> () );
   cout << mCharResult.GetCount () << endl;
   return 0;

}</source>