sort与qsort的区别与联系

 1 #include <algorithm>
 2 #include <functional>
 3 #include <array>
 4 #include <iostream>
 5 using namespace std;
 6 int cmpself(const void *a, const void *b){
 7     int arg1 = *static_cast<const int*>(a);
 8     int arg2 = *static_cast<const int*>(b);
 9 
10     if(arg1 < arg2) return -1;
11     if(arg1 > arg2) return 1;
12     return 0;
13     //return arg1 < arg2;//如果将上面的改为这个呢?就意味着前面元素大于后面元素,也就是降序排列了
14 }
15 int main()
16 {
17     //C++ sort 排序规则:前面元素大于后面元素,就返回降序结果;否则,返回升序结果.
18     std::array<int, 10> s = {5, 7, 4, 2, 8, 6, 1, 9, 0, 3};
19 
20     // sort using the default operator< sort默认升序排列
21     std::sort(s.begin(), s.end());
22     for (auto a : s) {
23         std::cout << a << " ";
24     }
25     std::cout << ‘\n‘;
26 
27     // sort using a standard library compare function object
28     //the former is greater than the later,降序排列
29     std::sort(s.begin(), s.end(), std::greater<int>());
30     for (auto a : s) {
31         std::cout << a << " ";
32     }
33     std::cout << ‘\n‘;
34 
35     // sort using a custom function object
36     struct {
37         bool operator()(int a, int b)
38         {
39             return a < b;//升序排列
40         }
41     } customLess;
42     std::sort(s.begin(), s.end(), customLess);
43     for (auto a : s) {
44         std::cout << a << " ";
45     }
46     std::cout << ‘\n‘;
47 
48     // sort using a lambda expression
49     std::sort(s.begin(), s.end(), [](int a, int b) {
50         return b < a;   //降序排列
51     });
52     for (auto a : s) {
53         std::cout << a << " ";
54     }
55     std::cout << ‘\n‘;
56 
57     //c++ qsort
58     int arr[] = {-2, 99, 0, -743, 2, INT_MIN+1, 4};
59     constexpr std::size_t elesize = sizeof(arr[0]);
60     constexpr std::size_t size = sizeof(arr) / sizeof(arr[0]);
61 
62     std::qsort(arr, size, sizeof(arr[0]), [](const void* a, const void* b)
63     {
64         int arg1 = *static_cast<const int*>(a);
65         int arg2 = *static_cast<const int*>(b);
66         //return arg1 < arg2; //error
67         if(arg1 < arg2) return -1;
68         if(arg1 > arg2) return 1;//需要注意的是,无论是C还是C++中的qsort,
69         return 0;
70 
71         //  return (arg1 > arg2) - (arg1 < arg2); // possible shortcut
72         //  return arg1 - arg2; // erroneous shortcut (fails if INT_MIN is present)
73     });
74 
75     for(int ai : arr)
76         std::cout << ai << ‘ ‘;
77     std::cout << ‘\n‘;
78     std::qsort(arr, size, sizeof(arr[0]), cmpself);
79     for(int ai : arr)
80         std::cout << ai << ‘ ‘;
81     std::cout << ‘\n‘;
82 }