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

A function object that computes an integer sum.

<source lang="cpp">

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

using namespace std; class sum : unary_function<int, void> { public:

 argument_type sum;
 sum() { sum = 0; }
 result_type operator()(argument_type i) {
 sum += i;
 }

}; int main() {

 vector<int> v;
 for(int i=1; i < 11; i++) v.push_back(i);
 for(unsigned i=0; i < v.size(); ++i){
   cout << v[i] << endl;
 }
 sum s;
 s = for_each(v.begin(), v.end(), sum());
 cout << "sum of v: " << s.sum << endl;
 return 0;

}

 </source>

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);

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

*/        
   
 </source>

Extends a unary_function

<source lang="cpp">

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

using namespace std; class MinMax : public unary_function<int, void>{ public:

 MinMax();
 void operator()(int elem);
 int min, max;

protected:

 bool first;

}; MinMax::MinMax() : min(-1), max(-1), first(true){} void MinMax::operator()(int elem){

 if (first) {
   min = max = elem;
 } else if (elem < min) {
   min = elem;
 } else if (elem > max) {
   max = elem;
 }
 first = false;

} int main(int argc, char** argv){

 vector<int> myVector;
 myVector.push_back(1);
 myVector.push_back(2);
 myVector.push_back(3);
 MinMax func;
 func = for_each(myVector.begin(), myVector.end(), func);
 cout << "The max is " << func.max << endl;
 cout << "The min is " << func.min << endl;
 return (0);

}

 </source>

Extends unary_function to do sum

<source lang="cpp">

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

using namespace std; class sum : unary_function<int, void> { public:

 argument_type sum;
 sum() { sum = 0; }
 result_type operator()(argument_type i) {
   sum += i;
 }

}; int main() {

 vector<int> v;
 for(int i=1; i < 11; i++) v.push_back(i);
 for(unsigned i=0; i < v.size(); ++i)
   cout << v[i] << endl;
 sum s;
 s = for_each(v.begin(), v.end(), sum());
 cout << "sum of v: " << s.sum << endl;
 v[4]= 99;
 s = for_each(v.begin(), v.end(), sum());
 cout << "sum of v is now: " << s.sum;
 return 0;

}

 </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;

} /* mean value: 4.5

*/
       
   
 </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: ");

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

*/
       
   
 </source>

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:            ");

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

*/        
   
 </source>

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;

} /* 1 2 3 4 5 6 7 8 9

*/        
   
 </source>

Use for_each with predicate

<source lang="cpp">

1. 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 << " ";

} /* 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

*/
       
   
 </source>