generate

Replaces each element with the result of an operation

Definition

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

Interface

#include <algorithm>
template < class ForwardIterator, class Generator >
   void generate(
      ForwardIterator first, 
      ForwardIterator last, 
      Generator gen
   );

Parameters:

Parameter	Description
first	A forward iterator addressing the position of the first element in the range to which values are to be assigned
last	A forward iterator addressing the position one past the final element in the range to which values are to be assigned
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

Generate algorithm uses a generator to generate each element of a range.

Return Value

None.

Complexity

The complexity is linear with last - first invocations of gen.

References

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

Example 1

Problem

This program illustrates the use of the STL generate() algorithm to fill a range of values in a vector of integers with 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 fill v with randomly generated integer values.";
  generate(v.begin(), v.end(), 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 the last half of v with new randomly generated integer values.";
  generate(v.begin()+5, v.end(), 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 fill v with randomly generated integer values.
Here are the revised contents of v:
41 18467 6334 26500 19169 15724 11478 29358 26962 24464

Finally, we fill the last half of v with new randomly generated integer values.
Here are the revised contents of v:
41 18467 6334 26500 19169 5705 28145 23281 16827 9961

References

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

Example 2

Problem

The following program demonstrates how to use generate() and generate_n() to insert or assign some random numbers.

Workings

#include <iostream>
#include <list>
#include <algorithm>
#include <cstdlib>

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
  PRINT_ELEMENTS(coll);

  //overwrite with five new random numbers
  generate (coll.begin(), coll.end(),    //destination range
                 rand);                  //new value generator
  PRINT_ELEMENTS(coll);

  return 0;
}

Solution

Output:

41 18467 6334 26500 19169
15724 11478 29358 26962 24464

References

Nicolai M. Josuttis: "The C++ Standard Library"

Definition

Interface

Description

Return Value

Complexity

References

Example 1

Example 2

See Also