C++ sort

之前看到过sort，今天又在程序中看到了。sort函数时STL中的函数，包含在头文件 #include <algorithm>  中。

参考： http://www.cplusplus.com/reference/algorithm/sort/

function template

<algorithm>

std::sort

default (1)

template <class RandomAccessIterator>  void sort (RandomAccessIterator first, RandomAccessIterator last);

custom (2)

template <class RandomAccessIterator, class Compare>  void sort (RandomAccessIterator first, RandomAccessIterator last, Compare comp);

Sort elements in range

Sorts the elements in the range [first,last) into ascending order.

The elements are compared using operator< for the first version, and comp for the second.

Equivalent elements are not guaranteed to keep their original relative order (see stable_sort).

Parameters

first, last

Random-access iterators to the initial and final positions of the sequence to be sorted. The range used is[first,last), which contains all the elements between first and last, including the element pointed by first but not the element pointed by last.
RandomAccessIterator shall point to a type for which swap is properly defined and which is both move-constructible and move-assignable.

comp

Binary function that accepts two elements in the range as arguments, and returns a value convertible tobool. The value returned indicates whether the element passed as first argument is considered to go before the second in the specific strict weak ordering it defines.
The function shall not modify any of its arguments.
This can either be a function pointer or a function object.

Return value

none

Example

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// sort algorithm example#include <iostream>     // std::cout#include <algorithm>    // std::sort#include <vector>       // std::vectorbool myfunction (int i,int j) { return (i<j); }struct myclass {  bool operator() (int i,int j) { return (i<j);}} myobject;int main () {  int myints[] = {32,71,12,45,26,80,53,33};  std::vector<int> myvector (myints, myints+8);               // 32 71 12 45 26 80 53 33  // using default comparison (operator <):  std::sort (myvector.begin(), myvector.begin()+4);           //(12 32 45 71)26 80 53 33  // using function as comp  std::sort (myvector.begin()+4, myvector.end(), myfunction); // 12 32 45 71(26 33 53 80)  // using object as comp  std::sort (myvector.begin(), myvector.end(), myobject);     //(12 26 32 33 45 53 71 80)  // print out content:  std::cout << "myvector contains:";  for (std::vector<int>::iterator it=myvector.begin(); it!=myvector.end(); ++it)    std::cout << ' ' << *it;  std::cout << '\n';  return 0;}

Output:

myvector contains: 12 26 32 33 45 53 71 80

Complexity

On average, linearithmic in the distance between first and last: Performs approximately N*log2(N) (where N is this distance) comparisons of elements, and up to that many element swaps (or moves).

Data races

The objects in the range [first,last) are modified.

Exceptions

Throws if any of the element comparisons, the element swaps (or moves) or the operations on iterators throws.
Note that invalid arguments cause undefined behavior.

算法耗时：N*log2(N) (where N is this distance) 。

其中重载的时候可以定义自己的比较函数，比如让他从小到大或从大大小排列：

bool compare(int a,int b){  return a<b; //升序排列，如果改为return a>b，则为降序}#include <algorithm>int main(){  int a[20]={2,4,1,23,5,76,0,43,24,65},i;  for(i=0;i<20;i++)  cout<<a[i]<<endl;  sort(a,a+20,compare);  for(i=0;i<20;i++)  cout<<a[i]<<endl;  return 0;}