c++ 生成容器元素生成随机数

// random_shuffle example
#include <iostream>     // cout
#include <algorithm>    // random_shuffle
#include <vector>       // vector
#include <ctime>        // time
#include <cstdlib>      // rand, srand
using namespace std;
// random generator function:
int myrandom (int i) { return rand()%i;}

int main () {
  srand ( unsigned ( time(0) ) );
  vector<int> myvector;

  // set some values:
  for (int i=1; i<10; ++i) myvector.push_back(i); // 1 2 3 4 5 6 7 8 9

  // using built-in random generator:
  random_shuffle ( myvector.begin(), myvector.end() );

 // print out content:
  cout << "using built-in random generator ,  myvector contains:";
  for (vector<int>::iterator it=myvector.begin(); it!=myvector.end(); ++it)
    cout << ' ' << *it;
  cout << '\n';

  // using myrandom:
  random_shuffle ( myvector.begin(), myvector.end(), myrandom);

  // print out content:
  cout << " using myrandom  ,  myvector contains:";
  for (vector<int>::iterator it=myvector.begin(); it!=myvector.end(); ++it)
    cout << ' ' << *it;

  cout << '\n';

  return 0;
}

using built-in random generator ,  myvector contains: 1 4 8 5 9 7 2 3 6
using myrandom  ,  myvector contains: 3 7 8 9 4 2 5 1 6