Question

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.

Answer 1

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); } }; 

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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; }