generate_n

Replaces n elements with the result of an operation

Definition

The generate_n() algorithm is defined in the standard header <algorithm> and in the nonstandard backward-compatibility header <algo.h>.

Interface

#include <algorithm>
template < class OutputIterator, class Diff, class Generator >
   void generate_n(
      OutputIterator first,
      Diff count,
      Generator gen
   );

Parameters:

Parameter	Description
first	An output iterator addressing the position of first element in the range to which values are to be assigned
count	A signed or unsigned integer type specifying the number of elements to be assigned a value by the generator function
gen	A function object that is called with no arguments that is used to generate the values to be assigned to each of the elements in the range

Description

The Generate_n algorithm does the same thing as http://www.codecogs.com/reference/computing/stl/algorithms/modifying/generate.php?showv=1"generate" but for n elements starting at first.

Return Value

None.

Complexity

The complexity is linear; count calls to the generator being required.

References

http://msdn.microsoft.com/en-us

Example 1

Problem

This program illustrates the functionality of generate_n() algorithm.

Workings

#include <vector>
#include <deque>
#include <algorithm>
#include <iostream>
#include <ostream>

using namespace std;

int main()
{
  // Assigning random values to vector integer elements
  vector <int> v1 ( 5 );
  vector <int>::iterator Iter1;
  deque <int> deq1 ( 5 );
  deque <int>::iterator d1_Iter;
   
  generate_n ( v1.begin ( ), 5 , rand );
   
  cout <<"Vector v1 is ( " ;
  for ( Iter1 = v1.begin( ) ; Iter1 != v1.end( ) ; Iter1++ )
    cout <<*Iter1<<" ";
  cout <<")."<<endl;

  // Assigning random values to deque integer elements
  generate_n ( deq1.begin ( ), 3 , rand );

  cout <<"Deque deq1 is ( " ;
  for ( d1_Iter = deq1.begin( ) ; d1_Iter != deq1.end( ) ; d1_Iter++ )
    cout <<*d1_Iter<<" ";
  cout <<")."<<endl;

  return 0;
}

Solution

Output:

Vector v1 is ( 41 18467 6334 26500 19169 ).
Deque deq1 is ( 15724 11478 29358 0 0 ).

References

http://msdn.microsoft.com/en-us

Example 2

Problem

This program illustrates the use of the STL generate_n() algorithm to fill a range of values starting at a given location in a vector of integers with a specified number of values generated by the rand() function from <cstdlib>.

Workings

#include <iostream>
#include <algorithm>
#include <vector>
#include <cstdlib>

using namespace std;

int main()
{
  vector<int> v(10);
  cout <<"\nHere are the initial contents of v:\n";
  for (vector<int>::size_type i=0; i<v.size(); i++)
    cout <<v.at(i)<<" ";

  cout <<"\nNow we generate 6 random integer values and place them into the vector,"
        " starting at location 3.";
  generate_n(v.begin()+2, 6, rand);
  cout <<"\nHere are the revised contents of v:\n";
  for (vector<int>::size_type i=0; i<v.size(); i++)
    cout <<v.at(i)<<" ";

  cout <<"\nFinally, we fill v with newly generated random integer values.";
  generate_n(v.begin(), (int)v.size(), rand);
  cout <<"\nHere are the revised contents of v:\n";
  for (vector<int>::size_type i=0; i<v.size(); i++)
    cout <<v.at(i)<<" ";

  return 0;
}

Solution

Output:

Here are the initial contents of v:
0 0 0 0 0 0 0 0 0 0

Now we generate 6 random integer values and place them into the vector, starting at location 3.
Here are the revised contents of v:
0 0 41 18467 6334 26500 19169 15724 0 0

Finally, we fill v with newly generated random integer values.
Here are the revised contents of v:
11478 29358 26962 24464 5705 28145 23281 16827 9961 491

References

http://www.smu.ca/academic/science/compsci/

Definition

Interface

Description

Return Value

Complexity

References

Example 1

Example 2

See Also