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==generate_n and 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.
*/
#include <iostream>
#include <list>
#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;
IntSequence seq(1); // integral sequence starting with 1
// insert values from 1 to 4
// - pass function object by reference
// so that it will continue with 5
generate_n<back_insert_iterator<list<int> >,
int, IntSequence&>(back_inserter(coll), // start
4, // number of elements
seq); // generates values
PRINT_ELEMENTS(coll);
// insert values from 42 to 45
generate_n (back_inserter(coll), // start
4, // number of elements
IntSequence(42)); // generates values
PRINT_ELEMENTS(coll);
// continue with first sequence
// - pass function object by value
// so that it will continue with 5 again
generate_n (back_inserter(coll), // start
4, // number of elements
seq); // generates values
PRINT_ELEMENTS(coll);

// continue with first sequence again
generate_n (back_inserter(coll), // start
4, // number of elements
seq); // generates values
PRINT_ELEMENTS(coll);
}
/*
1 2 3 4
1 2 3 4 42 43 44 45
1 2 3 4 42 43 44 45 5 6 7 8
1 2 3 4 42 43 44 45 5 6 7 8 5 6 7 8
*/

</source>

==Provide std::generate_n with predicate==

<source lang="cpp">

#include <iostream>
using std::cout;
using std::endl;
#include <algorithm>
#include <vector>
#include <iterator>
char nextLetter();
int main()
{
std::vector< char > chars( 10 );
std::ostream_iterator< char > output( cout, " " );
// generate values for first five elements of chars with nextLetter
std::generate_n( chars.begin(), 5, 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++;
}
/*

Vector chars after generating letters A-J:
A B C D E
*/
</source>

==Use generate_n 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.
*/
#include <cstdlib>
#include <iostream>
#include <vector>
#include <deque>
#include <list>
#include <set>
#include <map>
#include <string>
#include <algorithm>
#include <iterator>
#include <functional>
#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
PRINT_ELEMENTS(coll);
}
/*
41 18467 6334 26500 19169
*/
</source>

==Use std::generate_n to fill a vector by number==

<source lang="cpp">

#include <iostream>
using std::cout;
using std::endl;
#include <algorithm>
#include <vector>
#include <iterator>
char nextLetter();
int main()
{
std::vector< char > chars( 10 );
std::ostream_iterator< char > output( cout, " " );
// generate values for first five elements of chars with nextLetter
std::generate_n( chars.begin(), 5, 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++;
}
/*

Vector chars after generating letters A-J:
A B C D E
*/

</source>

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