generate_n (STL Samples)

Visual Studio 2005

Illustrates how to use the generate_n Standard Template Library (STL) function in Visual C++.

```
template<class OutputIterator, class Size, class Generator> inline
void generate_n(
OutputIterator First,
Size n,
Generator Gen
)
```

Remarks

Note

The class/parameter names in the prototype do not match the version in the header file. Some have been modified to improve readability.

The generate_n algorithm traverses the range [First, First + n), assigning to each element the value returned by Gen. Note that generate modifies the elements in the specified range.

Example

```// generate_n.cpp
// compile with: /EHsc
//
// Functions:
//   generate_n  - Fill a specified number of elements of a sequence
//                 using a generator function.
//
//   begin       - Returns an iterator that points to the first element
//                 in a sequence.
//
//   end         - Returns an iterator that points one past the end of
//                 a sequence.
//
//   size        - Returns the length of a sequence.

// disable warning C4786: symbol greater than 255 characters,
// okay to ignore
#pragma warning(disable: 4786)

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

using namespace std;

// return the next Fibonacci number in the
// Fibonacci series.
int Fibonacci(void)
{
static int r;
static int f1 = 0;
static int f2 = 1;
r = f1 + f2 ;
f1 = f2 ;
f2 = r ;
return f1 ;
}

int main()
{
const int VECTOR_SIZE = 15 ;

// Define a template class vector of integers
typedef vector<int > IntVector ;

//Define an iterator for template class vector of integer
typedef IntVector::iterator IntVectorIt ;

IntVector Numbers(VECTOR_SIZE) ;   //vector containing numbers

IntVectorIt start, end, it ;

int i ;

//Initialize vector Numbers
for(i = 0; i < VECTOR_SIZE; i++)
Numbers[i] = i * i ;

start = Numbers.begin() ;   // location of first
// element of Numbers

end = Numbers.end() ;       // one past the location
// last element of Numbers

cout << "Before calling generate_n" << endl ;

// print content of Numbers
cout << "Numbers { " ;
for(it = start; it != end; it++)
cout << *it << " " ;
cout << " }\n" << endl ;

// fill the specified range with a series of
// Fibonacci numbers using the Fibonacci function
generate_n(start + 5, Numbers.size() - 5, Fibonacci) ;

cout << "After calling generate_n" << endl ;

// print content of Numbers
cout << "Numbers { " ;
for(it = start; it != end; it++)
cout << *it << " " ;
cout << " }\n" << endl ;
}
```

Output

```Before calling generate_n
Numbers { 0 1 4 9 16 25 36 49 64 81 100 121 144 169 196  }

After calling generate_n
Numbers { 0 1 4 9 16 1 1 2 3 5 8 13 21 34 55  }```