C++ Tutorial/STL Algorithms Modifying sequence operations/generate — различия между версиями
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Текущая версия на 10:30, 25 мая 2010
Содержание
Illustrating the generic generate algorithm: Fill vector1 with 1, 4, 9, 16, ..., 100
#include <iostream>
#include <cassert>
#include <algorithm>
#include <vector>
using namespace std;
template <typename T>
class calc_square {
T i;
public:
calc_square(): i(0) {}
T operator()() { ++i; return i * i; }
};
int main()
{
vector<int> vector1(10);
generate(vector1.begin(), vector1.end(), calc_square<int>());
for (int j = 0; j < 10; ++j)
cout << vector1[j] << " ";
return 0;
}1 4 9 16 25 36 49 64 81 100
Int sequence
/* 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;
// insert values from 1 to 9
generate_n (back_inserter(coll), // start
9, // number of elements
IntSequence(1)); // generates values
PRINT_ELEMENTS(coll);
// replace second to last element but one with values starting at 42
generate (++coll.begin(), // start
--coll.end(), // end
IntSequence(42)); // generates values
PRINT_ELEMENTS(coll);
}1 2 3 4 5 6 7 8 9 1 42 43 44 45 46 47 48 9
Provide predicate for std::generate
#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 all elements of chars with nextLetter
std::generate( chars.begin(), chars.end(), 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 F G H I J
Use generate to insert five random numbers into a list
/* 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
// overwrite with five new random numbers
generate (coll.begin(), coll.end(), // destination range
rand); // new value generator
PRINT_ELEMENTS(coll);
}15724 11478 29358 26962 24464
Use std::generate to fill elements in a vector
#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 all elements of chars with nextLetter
std::generate( chars.begin(), chars.end(), 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 F G H I J
Using generate to fill values to a vector
#include <algorithm>
#include <vector>
#include <list>
#include <iostream>
int main (){
using namespace std;
vector <int> v (10);
generate ( v.begin (), v.end () , rand );
cout << "Elements in the vector of size " << v.size ();
for (size_t nCount = 0; nCount < v.size (); ++ nCount)
cout << v [nCount] << " ";
return 0;
}