C++/STL Algorithms Modifying sequence operations/generate
Содержание
Generate a sequence.
<source lang="cpp">
- include <iostream>
- include <vector>
- include <algorithm>
using namespace std; double pow_of_two(); int main() {
vector<double> v(5); generate(v.begin(), v.end(), pow_of_two); for(unsigned i=0; i < v.size(); ++i) cout << v[i] << endl; return 0;
} // A generator function that generates the powers of 2. double pow_of_two() {
static double val = 1.0; double t; t = val; val += val; return t;
}
</source>
Illustrating the generic generate algorithm: Fill vector1 with 1, 4, 9, 16, ..., 100
<source lang="cpp">
- 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
*/ </source>
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; // 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
*/ </source>
Provide predicate for std::generate
<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 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
*/ </source>
Use generate 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 // 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
*/ </source>
Use std::generate to fill elements in a vector
<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 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
*/ </source>