寫了挺多關於vector的操作了，正好工作中遇到對vector進行排序的問題，這裡就討論一下。

直接使用sort演算法，那就先了解一下：

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

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).
也就是所說的不穩定排序。

直接上程式碼：

#include <iostream>     // std::cout
 

#include <algorithm>    // std::sort
#include <vector>       // std::vector
#include <string>

bool 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';
    // Sorting the string vector
    std::vector<std::string> stringVec = { "John", "Bob", "Joe", "Zack", "Randy" };
    sort(stringVec.begin(), stringVec.end());

    for (std::string &s : stringVec)
        std::cout << s << " ";


    return 0;
}

//輸出：
myvector contains: 12 26 32 33 45 53 71 80
Bob Joe John Randy Zack

這個時候可以使用std::stable_sort()來實現穩定的排序了：
Sorts the elements in the range [first,last) into ascending order, like sort, but stable_sort preserves the relative order of the elements with equivalent values.

#include <iostream>     // std::cout
#include <algorithm>    // std::stable_sort
#include <vector>       // std::vector

bool compare_as_ints(double i, double j)
{
    return (int(i)<int(j));
}

int main() {
    double mydoubles[] = { 3.14, 1.41, 2.72, 4.67, 1.73, 1.32, 1.62, 2.58 };

    std::vector<double> myvector;

    myvector.assign(mydoubles, mydoubles + 8);

    std::cout << "using default comparison:";
    std::stable_sort(myvector.begin(), myvector.end());
    for (std::vector<double>::iterator it = myvector.begin(); it != myvector.end(); ++it)
        std::cout << ' ' << *it;
    std::cout << '\n';

    myvector.assign(mydoubles, mydoubles + 8);

    std::cout << "using 'compare_as_ints' :";
    std::stable_sort(myvector.begin(), myvector.end(), compare_as_ints);
    for (std::vector<double>::iterator it = myvector.begin(); it != myvector.end(); ++it)
        std::cout << ' ' << *it;
    std::cout << '\n';

    return 0;
}
//輸出：
using default comparison: 1.32 1.41 1.62 1.73 2.58 2.72 3.14 4.67
using 'compare_as_ints' : 1.41 1.73 1.32 1.62 2.72 2.58 3.14 4.67