为什么这个简单的Gecode示例不能编译？

Question

我正在尝试学习gecode，并尝试让示例发现的here工作。

// To use integer variables and constraints
#include <gecode/int.hh>
// To make modeling more comfortable
#include <gecode/minimodel.hh>  // To use search engines
#include <gecode/search.hh>
// To avoid typing Gecode:: all the time
using namespace Gecode;

class SendMoreMoney : public Space {
 protected:
  IntVarArray x;

 public:
  SendMoreMoney() : x(*this, 8, 0, 9) {
    IntVar s(x[0]), e(x[1]), n(x[2]), d(x[3]), m(x[4]), o(x[5]), r(x[6]),
        y(x[7]);
    rel(*this, s != 0);
    rel(*this, m != 0);
    distinct(*this, x);
    rel(*this,
        1000 * s + 100 * e + 10 * n + d + 1000 * m + 100 * o + 10 * r + e ==
            10000 * m + 1000 * o + 100 * n + 10 * e + y);
    branch(*this, x, INT_VAR_SIZE_MIN(), INT_VAL_MIN());
  }
  SendMoreMoney(SendMoreMoney& s) : Space(s) { x.update(*this, s.x); }
  virtual Space* copy() { return new SendMoreMoney(*this); }
  void print() const { std::cout << x << std::endl; }
};

int main() {
  SendMoreMoney* m = new SendMoreMoney;
  DFS<SendMoreMoney> e(m);
  delete m;
  while (SendMoreMoney s = e.next()) {
    s->print();
    delete s;
  }
}

我最终得到了以下编译错误。

error: no matching function for call to 'Gecode::IntVarArray::update(SendMoreMoney&, Gecode::IntVarArray&)'
   27 |             x.update(*this, s.x);
      |                                ^

和

error: invalid new-expression of abstract class type 'SendMoreMoney'
   30 |             return new SendMoreMoney(*this);
      |                

我不明白这些是从哪里来的。IntVarArray当然有一个update函数，它的第一个参数是一个Space对象，而SendMoreMoney继承自Space，那么有什么问题呢？这段代码与我发现的示例完全相同，因此它应该可以按原样工作。

Answer 1

e.next()返回克隆空间的指针(SendMoreMoney)。您必须使用while (SendMoreMoney* s = e.next())