Hi,

Can some one please explain the function FredPtr& operator= (const FredPtr& p) int the following lines of code ?

Qt Code: 
  1. class FredPtr;
  2.  
  3.  class Fred {
  4.  public:
  5.    Fred() : count_(0) /*...*/ { }  // All ctors set count_ to 0 !
  6.    ...
  7.  private:
  8.    friend class FredPtr;     // A friend class
  9.    unsigned count_;
  10.    // count_ must be initialized to 0 by all constructors
  11.    // count_ is the number of FredPtr objects that point at this
  12.  };
  13.  
  14.  class FredPtr {
  15.  public:
  16.    Fred* operator-> () { return p_; }
  17.    Fred& operator* ()  { return *p_; }
  18.    FredPtr(Fred* p)    : p_(p) { ++p_->count_; }  // p must not be NULL
  19.   ~FredPtr()           { if (--p_->count_ == 0) delete p_; }
  20.    FredPtr(const FredPtr& p) : p_(p.p_) { ++p_->count_; }
  21.    FredPtr& operator= (const FredPtr& p)
  22.        { // DO NOT CHANGE THE ORDER OF THESE STATEMENTS!
  23.            // (This order properly handles self-assignment)
  24.            // (This order also properly handles recursion, e.g., if a Fred contains FredPtrs)
  25.            Fred* const old = p_;//const pointer to a const Fred
  26.            p_ = p.p_;
  27.            ++p_->count_;
  28.  
  29.            //Will -- operator not change the count ? But Fred is const ???
  30.            if (--old->count_ == 0)  delete old;
  31.            return *this;
  32.          }
  33.  private:
  34.    Fred* p_;    // p_ is never NULL
  35.  };
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Thanks a lot.