指向成员函数的指针 - C++ std :: list sort

Question

如何将指向成员函数的指针传递给std :: list.sort()？

这可能吗？谢谢

struct Node {
       uint32_t ID;
       char *   Value;
};

class myClass {
          private:
            uint32_t  myValueLength;
          public:
            list<queueNode *> MyQueue;
            bool compare(Node * first, Node * second);
            bool doStuff();
}

bool myClass::compare(Node * first, Node * second) {
    unsigned int ii =0;
    while (ii < myValueLength)
    {
        if (first-> Value[ii] < second-> Value[ii]) 
        {
            return true;
        } else if (first-> Value[ii] > second-> Value[ii])
        {
            return false;
        }

        ++ii;
    }

    return false;
}

bool myClass::doStuff()
{
    list.sort(compare);
}

我想在类中使用长度变量,而不是在比较函数中使用strlen()(Value将始终具有相同的长度)

编辑:myValueLength不是我想从比较函数中访问的唯一变量我只是简化它以使示例更短.

Answer 1

阐述悲伤的反应,为什么不使用仿函数？例如:

struct Functor
{
  bool operator()( char * a, char * b )
    { return strcmp(a,b) < 0; }
};

然后你可以使用:

Functor f;
myList.sort(f);

您甚至可以通过定义operator()来将您的类用作Functor ...

class myClass {
  ...
  bool operator()( queueNode * a, queueNode * b )
  { return compare( a, b ); }

  void doStuff() { MyQueue.sort(*this); }
};

简单示例代码:

#include <iostream>
#include <list>
using namespace std;

  // Assumes  TYPE t; cout << t;  is valid.
template<class TYPE>
inline ostream & operator<< ( ostream & theOstream,
                              const list<TYPE> & theList )
{
  typename list<TYPE>::const_iterator listIterator = theList.begin();
  for ( int i = 0;   listIterator != theList.end();  listIterator ++, i ++ )
    theOstream << "    [" << i << "]:   \"" << (*listIterator) << "\"" << endl;
  return theOstream;
}

struct Functor
{
  bool operator()( const char * a, const char * b )
    { return strcmp(a,b) < 0; }
};

int
main()
{
  list<char*>  l;

    /* Load up some example test data... */
  char  s[3];
  s[2] = '\0';
  for (   s[0]='c'; s[0]>='a'; s[0]-- )
    for ( s[1]='c'; s[1]>='a'; s[1]--  )
      l.push_back(strdup(s));

    /* Show us that test data... */
  cout << l << endl;

    /* Sort list. */
  Functor f;
  l.sort(f);

    /* Show us what we have now... */
  cout << l << endl;
}

Answer 2

有可能的.你考虑过使用boost :: function吗？

list.sort( boost::bind( &myClass::compare, this, _1, _2 ) );

您的"比较"功能是否依赖于此数据？如果不是 - 你可能会简单地将'比较'功能变为静态.然后它会

list.sort( &myClass::compare );

您可以添加辅助结构来进行比较

list.sort( Comparer( myValueLength ) );

struct Comparer
{
    Comparer( uint32_t myValueLength ):
        length( myValueLength )
    {}

    bool operator() (Node * first, Node * second)
    {
        unsigned int ii =0;
        while (ii < length)
        {
            if (first-> Value[ii] < second-> Value[ii]) 
            {
                    return true;
            } else if (first-> Value[ii] > second-> Value[ii])
            {
                    return false;
            }

            ++ii;
        }

        return false;
    }


    uint32_t length;
};