The sample code below illustrates how to use the generate_n
STL function in Visual C++.
Required Header:
<algorithm>
template<class OutputIterator, class Size, class Generator> inline
void generate_n(OutputIterator first, Size n, Generator gen)
Note: The class/parameter names in the prototype do not match the version in the header file. Some have been modified to improve readability.
Description:
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.
Sample Code:
//////////////////////////////////////////////////////////////////////
//
// Compile options needed: /GX
//
// generate_n.cpp : Illustrates how to use the generate_n function.
//
// 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 character,
// 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 ;
}
void 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 ;
}
Program Output is:
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 }