c++中在执行期指定排序准则

 1 //定义排序准则的仿函数
 2 template<class T>
 3 class RuntimeCmp
 4 {
 5 public:
 6     enum cmp_mode { _normal, _reverse};
 7 public:
 8     RuntimeCmp(cmp_mode m = _normal) : mode(m){}
 9
10     bool operator() (const T &t1, const T &t2) const{ return mode == _normal ? t1 < t2 : t2 < t1;}//重载（）操作符
11     bool operator== (const RuntimeCmp &rc){ return mode == rc.mode;}
12
13 private:
14     cmp_mode mode;
15 };
16
17 int main()
18 {
19     typedef set<int, RuntimeCmp<int> > IntSet;
20     IntSet coll1;
21     coll1.insert(4);
22     coll1.insert(7);
23     coll1.insert(5);
24     coll1.insert(1);
25     coll1.insert(6);
26     coll1.insert(2);
27     coll1.insert(5);
28     cout << "coll1: ";
29     copy(coll1.begin(), coll1.end(), ostream_iterator<int>(cout, " "));
30     cout << endl;
31
32     RuntimeCmp<int> reverse_order(RuntimeCmp<int>::_reverse);
33
34     IntSet coll2(reverse_order);
35     coll2.insert(4);
36     coll2.insert(7);
37     coll2.insert(5);
38     coll2.insert(1);
39     coll2.insert(6);
40     coll2.insert(2);
41     coll2.insert(5);
42
43     cout << "coll2: ";
44     copy(coll2.begin(), coll2.end(), ostream_iterator<int>(cout, " "));
45     cout << endl;
46
47     coll1 = coll2;
48     coll1.insert(3);
49     cout << "coll1: ";
50     copy(coll1.begin(), coll1.end(), ostream_iterator<int>(cout, " "));
51     cout << endl;
52
53     //测试coll1和coll2排序准则是否相同
54     if(coll1.value_comp() == coll2.value_comp())
55     {
56         cout << "coll1 and coll2 have same sorting criterion" << endl;
57     }
58     else
59     {
60          cout << "coll1 and coll2 have different sorting criterion" << endl;
61     }

程序输出：

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

注：赋值操作符同时也赋值了排序准则

详见c++标准程序库