problem with find function in Vector of Structure in C++

I a开发者_C百科m trying to use the "find" function here. For that here's the code for the '==' operator. But I am getting a "too many parameters for this operator function" error at the word "operator".

Can anyone kindly help me out ? Thanks.

struct gr_log
{
   string name;
   string category;
   string description;
   float cost;
   bool operator==(const gr_log& l, const gr_log& r) const

   {
           return l.name == r.name;
  }

};

And:

vector<gr_log>::iterator it;
it = find (grocery.begin(), grocery.end(), "Sugar");

A member operator only takes one argument:

struct gr_log
{
   string name;
   string category;
   string description;
   float cost;
   bool operator==(const gr_log& r)
   {
       return name == r.name;
   }
};

Alternatively, you could write a friend operator:

struct gr_log
{
   string name;
   string category;
   string description;
   float cost;
   friend bool operator==(const gr_log& l, const gr_log& r)
   {
       return l.name == r.name;
   }
};

Also, you'll need to perform a find using an instance of gr_log because you can't compare a gr_log with a string like you're trying to do:

it = find (grocery.begin(), grocery.end(), gr_log("Sugar"));

Try this:

struct gr_log
{
   string name;
   string category;
   string description;
   float cost;
   bool operator==(const string& name) {
    return name == this->name;
  }
};

This creates a == operator (using the correct syntax for member variable; it compares the explicit argument to the implicit this), which compares a gr_log to a string. Since your std::find call uses a string as a comparison object, you should be good to go.

As an alternative, you can define equality operators outside of your class:

struct gr_log
{
   string name;
   string category;
   string description;
   float cost;
};
inline bool operator==(const gr_log& gr, const string& name) {
   return name == gr.name;
}
inline bool operator==(const sting& name, const gr_log& gr) {
   return name == gr.name;
}

Note 1: The inline keywords should be there if you are putting these in a header file, but not if you are putting them in a source file.

Note 2: Specifying both operator functions allows for the commutative property of equality.

Finally, in case this hasn't been hashed over enough -- the member equality operator takes one parameter, the non-member equality operator takes two.

operator == should not be a member of your structure. Or if it is, it should take 1 argument and compare it with this:

struct gr_log
{ ...
bool operator==(const gr_log& l) const {return name == r.name;}
}
//or outside of the structure
bool operator==(const gr_log& l, const gr_log& r) 
{
       return l.name == r.name;
}

You have two choices: either a function bool operator==(a,b) outside of the struct, or a bool operator==(other) inside the struct.