本文章转载自：ffhajbq特别感谢原作者。

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这两个方法都用来将指定容器的元素根据指定的predicate函数分成两个子序列，其中满足predicate()函数的，即返回值为true的作为第一个序列[v.begin(), bound), 而[bound, v.end())的作为第二个序列。

两个方法的区别在于， partition()对于两个子序列中的元素并不排序，而stable_partition()则对两个子序列的元素也进行排序。

BidirectionalIterator partition ( BidirectionalIterator first, BidirectionalIterator last, Predicate pred );
BidirectionalIterator stable_partition ( BidirectionalIterator first, BidirectionalIterator last, Predicate pred );
参数表说明：

Parameters

first, last  第一个和第二个参数说明给定源容器的范围 [first, last)

Bidirectional iterators to the initial and final positions of the sequence to be partitioned. 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.

pred 第三个参数给定进行分组的规则函数 布尔型返回值 对于返回true的所有元素作为第一个子序列，对于返回false的所有元素作为第二个子序列

Unary predicate taking an element in the range as argument, and returning a value indicating the falsehood (with  false, or a zero value) or truth ( true, or non-zero) of some condition applied to it. This can either be a pointer to a function or an object whose class overloads  operator().

Return value 返回值是 指向第二个子序列的首元素迭代器...

An iterator that points to the first element of the second group of elements. For all the elements in this second group, pred return false.
举例说明：

#include <iostream>
 #include <vector>
 #include <algorithm>
 
 using namespace std;
 
 bool IsOdd(int i)
 {
     return (i%2 == 1);
 }
 
 int main()
 {
     vector<int> v;
     for(int i = 0; i < 10; i++)
         v.push_back(i);
 
     cout<<"The original elements in the vector are: "<<endl;
     vector<int>::iterator it, bound;
 
     for(it = v.begin(); it != v.end(); it++)
         cout<<*it<<" ";
     cout<<endl;
 
     cout<<"First use the function partition() to separate all elements into 2 groups without ordering: "<<endl;
     //use partition to separate the vector into 2 parts...
     bound = partition(v.begin(), v.end(), IsOdd);
 
     cout << "All odd elements in the vector are:" <<endl;
     for(it = v.begin(); it != bound; it++)
         cout<<*it<<" ";
     cout<<endl;
 
     cout<< "All even elements in the vector are:" <<endl;
     for(it = bound; it != v.end(); it++)
         cout<<*it<<" ";
     cout<<endl;
 
     v.clear();
     for(int i = 0; i < 10; i++)
     v.push_back(i);
 
     cout<<"Secondly use the function stable_partition() to separate all elements into 2 groups with ordering: "<<endl;
     //use stable_partition to separate the vector into 2 parts...
     bound = stable_partition(v.begin(), v.end(), IsOdd);
     
         cout << "All odd elements in the vector are:" <<endl;
     for(it = v.begin(); it != bound; it++)
         cout<<*it<<" ";
     cout<<endl;
 
     cout<< "All even elements in the vector are:" <<endl;
     for(it = bound; it != v.end(); it++)
         cout<<*it<<" ";
     cout<<endl;
     
     return 0;
 }
输出结果：
The original elements in the vector are:
 0 1 2 3 4 5 6 7 8 9
 First use the function partition() to separate all elements into 2 groups without ordering:
 All odd elements in the vector are:
 9 1 7 3 5
 All even elements in the vector are:
 4 6 2 8 0
 Secondly use the function stable_partition() to separate all elements into 2 groups with ordering:
 All odd elements in the vector are:
 1 3 5 7 9
 All even elements in the vector are:
 0 2 4 6 8
分析：
这一次取的数组有点特殊，不能明显分辨两个函数的区别，我们使用随机数发生器产生一个数组vInt，vInt2 = vInt;
vInt = {2 6 3 8 4 5 9 7 1 0}
使用stable_partition函数对vInt分类，结果为：
{3 5 9 7 1；2 6 8 4 0}
而使用partition函数对vInt分类，结果为：
{1 7 3 9 5；4 8 6 2 0}
可以看到，stable函数可以保证在分类过程中不改变原来同一类元素的相对位置。