C++ Tutorial/STL Algorithms Modifying sequence operations/generate

Illustrating the generic generate algorithm: Fill vector1 with 1, 4, 9, 16, ..., 100

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

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

using namespace std; template <typename T> class calc_square {

 T i;
public:
 calc_square(): i(0) {}
 T operator()() { ++i; return i * i; }

}; int main() {

 vector<int> vector1(10);
 generate(vector1.begin(), vector1.end(), calc_square<int>());
 for (int j = 0; j < 10; ++j)
   cout << vector1[j] << " ";
 return 0;

}</source>

1 4 9 16 25 36 49 64 81 100

Int sequence

<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;

}

class IntSequence {

 private:
   int value;
 public:
   // constructor
   IntSequence (int initialValue) : value(initialValue) {
   }
   // ""function call""
   int operator() () {
       return value++;
   }

}; int main() {

   list<int> coll;
   // insert values from 1 to 9
   generate_n (back_inserter(coll),    // start
               9,                      // number of elements
               IntSequence(1));        // generates values
   PRINT_ELEMENTS(coll);
   // replace second to last element but one with values starting at 42
   generate (++coll.begin(),           // start
             --coll.end(),             // end
             IntSequence(42));         // generates values
   PRINT_ELEMENTS(coll);

}</source>

1 2 3 4 5 6 7 8 9
1 42 43 44 45 46 47 48 9

Provide predicate for std::generate

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

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

char nextLetter(); int main() {

  std::vector< char > chars( 10 );
  std::ostream_iterator< char > output( cout, " " );
   // generate values for all elements of chars with nextLetter
  std::generate( chars.begin(), chars.end(), nextLetter );
  cout << "\n\nVector chars after generating letters A-J:\n";
  std::copy( chars.begin(), chars.end(), output );
  cout << endl;
  return 0;

} // generator function returns next letter (starts with A) char nextLetter() {

  static char letter = "A";
  return letter++;

}</source>

Vector chars after generating letters A-J:
A B C D E F G H I J

Use generate to insert five random numbers into a 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 <cstdlib>
2. include <iostream>
3. include <vector>
4. include <deque>
5. include <list>
6. include <set>
7. include <map>
8. include <string>
9. include <algorithm>
10. include <iterator>
11. include <functional>
12. 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; int main() {

   list<int> coll;
   // insert five random numbers
   generate_n (back_inserter(coll),      // beginning of destination range
               5,                        // count
               rand);                    // new value generator
   // overwrite with five new random numbers
   generate (coll.begin(), coll.end(),   // destination range
             rand);                      // new value generator
   PRINT_ELEMENTS(coll);

}</source>

15724 11478 29358 26962 24464

Use std::generate to fill elements in a vector

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

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

char nextLetter(); int main() {

  std::vector< char > chars( 10 );
  std::ostream_iterator< char > output( cout, " " );
   // generate values for all elements of chars with nextLetter
  std::generate( chars.begin(), chars.end(), nextLetter );
  cout << "\n\nVector chars after generating letters A-J:\n";
  std::copy( chars.begin(), chars.end(), output );
  cout << endl;
  return 0;

} // generator function returns next letter (starts with A) char nextLetter() {

  static char letter = "A";
  return letter++;

}</source>

Vector chars after generating letters A-J:
A B C D E F G H I J

Using generate to fill values to a vector

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

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

int main (){

   using namespace std;
   vector <int> v (10);
   generate ( v.begin (), v.end () , rand );    
   cout << "Elements in the vector of size " << v.size ();
   for (size_t nCount = 0; nCount < v.size (); ++ nCount)
       cout << v [nCount] << " ";
   return 0;

}</source>