CODEWITHSUNDEEP
c++
user1952500
user1952500

Reputation: 6781

Opaque Handle in C++

I am implementing an opaque data structure that is internally an array of opaque data structures. Let's call them records. There will be multiple queries to different fields of a record each with the same key. I have a list of APIs of this form:

QueryFieldX(KEY key, FieldX& Data)

Each query currently searches through the records with the key and then gets the Data.

I want to change it to the following form:

GetHandleToRecord(KEY key, MYHANDLE handle);
QueryFieldX(MYHANDLE handle, FieldX& Data);

The advantage is that searching every single time through the records is eliminated. I can implement a MYHANDLE myself but I want to know if there is a good library / data structure / primitive in C++ that gives me an opaque handle that I can use.

Upvotes: 1

Views: 970

Answers (1)

Drew Dormann
Drew Dormann

Reputation: 63946

A handle is typically an obfuscated pointer to the data, such as this.

typedef void* MYHANDLE;

You would explicitly reinterpret_cast the pointer as needed, such as in this code.

MYHANDLE GetHandleToRecord(KEY key)
{
   FieldX *the_result;

   // (assign the correct pointer to the_result)

   return reinterpret_cast<MYHANDLE>( the_result );
}

QueryFieldX(MYHANDLE handle, FieldX& Data)
{
    Data = *reinterpret_cast<FieldX*>( handle )
}

In your case, the handle could also be an array index, or a key to a std::map. Anything that can later be converted back to the data itself.

Upvotes: 1

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