STL - 容器 - 运行期指定排序准则

RuntimeCmp.hpp

#include <set>

using namespace std;

// type for runtime sorting criterion
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
// - member function for any element type
template <typename T>
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) const
{
return mode == rc.mode;
}
};

// type of a set that uses this sorting criterion
typedef set<int, RuntimeCmp> IntSet;

#include <iostream>
#include <set>
#include <algorithm>
#include <iterator>
#include <functional>
#include "SetTest.h"
#include "../../Core/RuntimeCmp.hpp"
#include "../../Core/print.hpp"

using namespace std;

void SetTest::runtimeCompare()
{
// create, fill, and print set with normal element order
// - uses default sorting criterion
IntSet coll1 = { 4, 7, 5, 1, 6, 2, 5 };
PRINT_ELEMENTS(coll1, "coll1: ");

// create sorting criterion with reverse element order
RuntimeCmp reverse_order(RuntimeCmp::reverse);

// create, fill, and print set with reverse element order
IntSet coll2(reverse_order);
coll2 = { 4, 7, 5, 1, 6, 2, 5 };
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 the same sorting criterion"
<< endl;
}
else
{
cout << "coll1 and coll2 have a different sorting criterion"
<< endl;
}
}

void SetTest::run()
{
printStart("runtimeCompare()");
runtimeCompare();
printEnd("runtimeCompare()");
}

运行结果:

---------------- runtimeCompare(): Run Start ----------------
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 the same sorting criterion
---------------- runtimeCompare(): Run End ----------------