指向成员函数的指针 - C ++ std :: list sort [英] Pointer to member functions - C++ std::list sort

问题描述

我如何传递指向成员函数的指针到std :: list.sort（）？

这是否可能？感谢

  struct Node {
 uint32_t ID; 
 char * Value; 
}; 
 
类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strlen ）在比较函数内（该值将始终是相同的长度）

编辑：myValueLength不是我想在比较函数内访问的唯一变量我只是简化了它使示例更短。

解决方案

阐述 grieve的响应，为什么不使用函子？例如：

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

然后您可以使用：

  Functor f; 
 myList.sort（f）; 
  

您甚至可以通过定义operator（）...

  class myClass {
 ... 
 bool operator（）（queueNode * a，queueNode * b）
 {return compare（a，b）; } 
 
 void doStuff（）{MyQueue.sort（* this）; } 
}; 
  

---

代码：

  #include< iostream> 
 #include< list> 
 using namespace std; 
 
 //假设TYPE t; cout < t;已验证。 
 template< class TYPE> 
 inline ostream&运算符<< （ostream& theOstream，
 const list< TYPE& theList）
 {
 typename list< TYPE> :: const_iterator listIterator = theList.begin（）; 
 for（int i = 0; listIterator！= theList.end（）; listIterator ++，i ++）
 thestream< [< 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; 
 
 / *加载一些示例测试数据... * / 
 char s [3]; 
 s [2] ='\0'; （s [0] ='c'; s [0]> ='a'; s [0]  - ）
 for（s [1] ='c'; s [ 1]> ='a'; s [1]  - ）
 l.push_back（strdup（s））; 
 
 / *告诉我们测试数据... * / 
 cout< 1<< endl 
 
 / *排序列表。 * / 
 Functor f; 
 l.sort（f）; 
 
 / *告诉我们我们现在有什么... * / 
 cout< 1<< endl 
} 
  

How do i pass a pointer to a member function to std::list.sort()?

Is this possible? Thanks

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);
}

I want to use a length variable from within the class instead of doing strlen() within the compare function (The Value will always be the same length)

Edit: The myValueLength was not the only variable i wanted to access from within the comparison function I just simplified it to make the example shorter.

解决方案

Elaborating on grieve's response, why not use a functor? E.g.:

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

Then you could just use:

Functor f;
myList.sort(f);

You could even use your class as the Functor by defining operator()...

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

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

---

Simple example code:

#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;
}

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