Mega Code Archive
Set comparison
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/* 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 <set>
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;
}
// type for sorting criterion
template <class T>
class RuntimeCmp {
public:
enum cmp_mode {normal, reverse};
private:
cmp_mode mode;
public:
// constructor for sorting criterion
// - default criterion uses value normal
RuntimeCmp (cmp_mode m=normal) : mode(m) {
}
// comparison of elements
bool operator() (const T& t1, const T& t2) const {
return mode == normal ? t1 < t2 : t2 < t1;
}
// comparison of sorting criteria
bool operator== (const RuntimeCmp& rc) {
return mode == rc.mode;
}
};
// type of a set that uses this sorting criterion
typedef set<int,RuntimeCmp<int> > IntSet;
// forward declaration
void fill (IntSet& set);
int main()
{
// create, fill, and print set with normal element order
// - uses default sorting criterion
IntSet coll1;
fill(coll1);
PRINT_ELEMENTS (coll1, "coll1: ");
// create sorting criterion with reverse element order
RuntimeCmp<int> reverse_order(RuntimeCmp<int>::reverse);
// create, fill, and print set with reverse element order
IntSet coll2(reverse_order);
fill(coll2);
PRINT_ELEMENTS (coll2, "coll2: ");
// assign elements AND sorting criterion
coll1 = coll2;
coll1.insert(3);
PRINT_ELEMENTS (coll1, "coll1: ");
// just to make sure...
if (coll1.value_comp() == coll2.value_comp()) {
cout << "coll1 and coll2 have same sorting criterion"
<< endl;
}
else {
cout << "coll1 and coll2 have different sorting criterion"
<< endl;
}
}
void fill (IntSet& set)
{
// fill insert elements in random order
set.insert(4);
set.insert(7);
set.insert(5);
set.insert(1);
set.insert(6);
set.insert(2);
set.insert(5);
}
coll1: 1 2 4 5 6 7
coll2: 7 6 5 4 2 1
coll1: 7 6 5 4 3 2 1
coll1 and coll2 have same sorting criterion
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