Computer Science Canada

Parameter Passing Help
Author:  jin [ Fri Mar 02, 2007 1:01 am ]
Post subject:  Parameter Passing Help
Hey i have a function that has parameters of an int and a pointer to an object. i am passing in an int and an address of an object. the function finds the object with the int value. i would like to change the address of the object being passed in to the to the one in the function. how would i go about doing this.

PS: cannot change parameters to references and cannot change return type.

if u dont understand that

in main
code:
Database.retrieve(x, &tempRecord)


the function
code:
retrieve(unsigned int studentNum, studentRecord* searchRecord)
{
        for (int index = 0; index < _next_index; index++)
        {
                if (_arrayDB[index]->getStudentNumber() == studentNum)
                {
                        searchRecord = _arrayDB[index];
                }
        }
}


i want tempRecord in main to have address of _arrayDB[index]

appreciate any help
Author:  abcdefghijklmnopqrstuvwxy [ Sun Mar 04, 2007 7:23 pm ]
Post subject:  RE:Parameter Passing Help
code:

retrieve(unsigned int studentNum, studentRecord* searchRecord //a pointer named searchRecord points to the address of tempRecord)
{
   for (int index = 0; index < _next_index // where is this declared?; index++)
   {
      if (_arrayDB[index]->getStudentNumber() == studentNum)
      {
         searchRecord = _arrayDB[index]; //now the pointer searchRecord points to the studentRecord* located at index.  We haven't changed tempRecord.
         break;
      }
   }
}


But what is tempRecord exactly? It is an object you created on the stack. Not a pointer. When you pass it's address to this function you can manipulate that object, but you can't turn that object into a pointer by supplying its address.

In order for tempRecord to have an address which can be changed you need to declare it as a pointer, not an object.

code:

studentRecord* tempRecord = new studentRecord;

//then pass it to the function like so:

Database.retrieve(num, tempRecord);


But you mentioned you cannot change any parameters. Well, without changing any parameters you CANNOT change the address of tempRecord to anything, because it is not a poitner. But you could make the value of tempRecord equal the value of _arrayDB[index]. How? First be sure to overload the = operator in your class declaration. Then,

code:

*searchRecord = *_arrayDB[index];


If you don't know about overloading the = operator than google it or find the answer in these forums. wtd covered it a few times I think in the tutorial section.

:


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