C++ Tutorial/STL Algorithms Modifying sequence operations/generate n — различия между версиями
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Текущая версия на 13:30, 25 мая 2010
Содержание
- 1 Demonstrating fill, fill_n, generate, and generate_n Standard Library methods.
- 2 generate_n and int sequence
- 3 Provide std::generate_n with predicate
- 4 Use generate_n to insert five random numbers into a list
- 5 Use generate_n to list to Random Values
- 6 Use std::generate_n to fill a vector by number
Demonstrating fill, fill_n, generate, and generate_n Standard Library methods.
<source lang="cpp">#include <iostream>
- include <algorithm>
- include <vector>
using namespace std; char nextLetter(); int main() {
vector< char > chars( 10 ); fill( chars.begin(), chars.end(), "5" ); fill_n( chars.begin(), 5, "A" ); generate( chars.begin(), chars.end(), nextLetter ); generate_n( chars.begin(), 5, nextLetter ); cout << endl; return 0;
} char nextLetter() {
static char letter = "A"; return letter++;
}</source>
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);
}</source>
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
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++;
}</source>
Vector chars after generating letters A-J: A B C D E
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);
}</source>
41 18467 6334 26500 19169
Use generate_n to list to Random Values
<source lang="cpp">#include <algorithm>
- include <vector>
- include <list>
- include <iostream>
using namespace std; int main (){
list <int> l (10); generate_n (l.begin (), 5, rand); cout << "Elements in the list of size: " << l.size (); list <int>::const_iterator li; for ( li = l.begin (); li != l.end (); ++ li ) cout << *li << " ";
return 0;
}</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++;
}</source>
Vector chars after generating letters A-J: A B C D E