c++ sort 类的一点区别

STL的sort()算法，数据量大时采用Quick Sort，分段递归排序，一旦分段后的数据量小于某个门槛，为避免Quick Sort的递归调用带来过大的额外负荷，就改用Insertion Sort。如果递归层次过深，还会改用Heap Sort。STL sort算法(以上三种算法的综合) -- Introspective Sorting(内省式排序)。

I）Sort函数包含在头文件为#include的c++标准库中！
II）Sort函数有三个参数：
（1）第一个是要排序的数组的起始地址。
（2）第二个是结束的地址（最后一位要排序的地址）
（3）第三个参数是排序的方法，可以是从大到小也可是从小到大，还可以不写第三个参数，此时默认的排序方法是从小到大排序。

STL里面有个sort函数，可以直接对数组排序，复杂度为n*log2(n)。

使用第一个版本是对[first,last)进行升序排序，默认操作符为"<"，第二个版本使用comp函数进行排序控制，comp包含两个在[first,last)中对应的值，如果使用"<"则为升序排序，如果使用">"则为降序排序，分别对int、float、char以及结构体排序:

sort_main函数

#include "stdafx.h"
#include
#include
#include
#include 
using namespace std;

bool compare(const string &a, const string &b){
	return a > b;
}
bool cmp(const int &a, const int &b){
	return a > b;
}
int _tmain(int argc, _TCHAR* argv[])
{
	vector res = { "ABC", "ACB", "BAC", "BCA", "CAB", "CBA"};
	vector B = { 1, 2, 3, 4, 5 };
	for (int i = 0; i < res.size(); i++){
		cout << res[i] << " ";
	}
	cout << endl;
	for (int i = 0; i < B.size(); i++){
		cout << B[i] << " ";
	}
	cout << endl;
	sort(B.begin(), B.end(), cmp);
	sort(res.begin(), res.end(), compare);
	for (int i = 0; i < res.size(); i++){
		cout << res[i] << " ";
	}
	cout << endl;
	for (int i = 0; i < B.size(); i++){
		cout << B[i] << " ";
	}
	cout << endl;
	system("pause");
	return 0;
}

输出：

ABC ACB BAC BCA CAB CBA
1 2 3 4 5
CBA CAB BCA BAC ACB ABC
5 4 3 2 1

sort_class函数

class Test{
public:
	static bool compare(const string &a, const string &b){
		return a > b;
	}
	static bool cmp(const int &a, const int &b){
		return a > b;
	}
	void test(){
		vector res = { "ABC", "ACB", "BAC", "BCA", "CAB", "CBA" };
		vector B = { 1, 2, 3, 4, 5 };
		for (int i = 0; i < res.size(); i++){
			cout << res[i] << " ";
		}
		cout << endl;
		for (int i = 0; i < B.size(); i++){
			cout << B[i] << " ";
		}
		cout << endl;
		sort(B.begin(), B.end(), cmp);
		sort(res.begin(), res.end(), compare);
		for (int i = 0; i < res.size(); i++){
			cout << res[i] << " ";
		}
		cout << endl;
		for (int i = 0; i < B.size(); i++){
			cout << B[i] << " ";
		}
		cout << endl;
	}
};
int _tmain(int argc, _TCHAR* argv[])
{
	Test t;
	t.test();
	system("pause");
	return 0;
}

输出：

ABC ACB BAC BCA CAB CBA
1 2 3 4 5
CBA CAB BCA BAC ACB ABC
5 4 3 2 1

这里sort_main函数与sort_class函数，有一点区别的是

sort_main函数要申明为

bool compare(const string &a, const string &b){
return a > b;
}

sort_class函数要申明为

static bool compare(const string &a, const string &b){
return a > b;
}

sort_class函数没有申明static,会出错（没有深入研究，先记录下来）

错误 4error C2780: “void std::sort(_RanIt,_RanIt)”: 应输入 2 个参数，却提供了 3 个

错误 3error C3867: “Test::compare”:  函数调用缺少参数列表；请使用“&Test::compare”创建指向成员的指针

gcc下编译，sort_class函数没有申明static,也会出错

In file included from a.cc:2:
./solution.h:10:32: error: reference to non-static member function must be called
sort(res.begin(), res.end(), compare);
1 error generated.

gcc下编译，sort_class函数申明static，但是参数没有申明为const 也会出错

static bool compare(string &a, string &b)){
return a > b;
}

In file included from a.cc:1:
In file included from /home/web/newjudge/include/nc_tools.h:5:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/algorithm:62:
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/bits/stl_algo.h:2287:28: error: binding of reference to type 'basic_string<[3 * ...]>' to a value of type 'const basic_string<[3 * ...]>' drops qualifiers
while (__comp(*__first, __pivot))~~~~~~
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/bits/stl_algo.h:2319:19: note: in instantiation of function template specialization 'std::__unguarded_partition<__gnu_cxx::__normal_iterator<std::basic_string *, std::vector > >, std::basic_string, bool (*)(std::basic_string &, std::basic_string &)>' requested here
return std::__unguarded_partition(__first + 1, __last, *__first, __comp);
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/bits/stl_algo.h:2360:11: note: in instantiation of function template specialization 'std::__unguarded_partition_pivot<__gnu_cxx::__normal_iterator > >, bool (*)(std::basic_string &, std::basic_string &)>' requested here
std::__unguarded_partition_pivot(__first, __last, __comp);
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/bits/stl_algo.h:5512:9: note: in instantiation of function template specialization 'std::__introsort_loop<__gnu_cxx::__normal_iterator > >, long, bool (*)(std::basic_string &, std::basic_string &)>' requested here
std::__introsort_loop(__first, __last,
./solution.h:10:3: note: in instantiation of function template specialization 'std::sort<__gnu_cxx::__normal_iterator > >, bool (*)(std::basic_string &, std::basic_string &)>' requested here
sort(res.begin(), res.end(), compare);
In file included from a.cc:1:
In file included from /home/web/newjudge/include/nc_tools.h:5:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/algorithm:62:
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/bits/stl_algo.h:2290:18: error: binding of reference to type 'basic_string<[3 * ...]>' to a value of type 'const basic_string<[3 * ...]>' drops qualifiers
while (__comp(__pivot, *__last))
2 errors generated.