Read Binary object into an array?

kraigballa (150)
I know the topic may be hard to understand, but I am basically trying to take an already stored binary I/O file (which has 5 loan objects in it), read the results and store them into an array. This way I can add 5 to each byte.

Here's how I stored them:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
 
fstream loanf;// Create stream object
	loanf.open("Exercise13_6.dat", ios::out | ios::binary);

	// Instantiate loan objects
	Loan loan1(5.3, 10, 20000);
	Loan loan2(3.0, 5, 10000);
	Loan loan3(10.9, 7, 15000);
	Loan loan4(21.3, 5, 10000);
	Loan loan5(2.3, 3, 5000);

	// Write binary into file
	loanf.write(reinterpret_cast<char*> (&loan1), sizeof(Loan));
	loanf.write(reinterpret_cast<char*> (&loan2), sizeof(Loan));
	loanf.write(reinterpret_cast<char*> (&loan3), sizeof(Loan));
	loanf.write(reinterpret_cast<char*> (&loan4), sizeof(Loan));
	loanf.write(reinterpret_cast<char*> (&loan5), sizeof(Loan));

	loanf.close();


Here's how I read it..in a different cpp file: (this works)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
 
// Read array from the file
	fstream binaryio; // Create stream object

	// Read loan back from the file
	binaryio.open(inputFilename, ios::in | ios::binary);

	Loan newLoan;

	binaryio.seekg (0, ios::end);
	int length = binaryio.tellg() / sizeof(int);
	binaryio.seekg(0); //to return the file pointer to the beginning

	int *result = new int [length];

	// Display array
	for (int i = 0; i < length; i++)
	{
		// Reading one int at a time
		binaryio.read(reinterpret_cast<char*> (&newLoan), sizeof(Loan));
		if ( binaryio.eof() ) // Will check for end of file
			 break; // Exit from the while if end of file
		displayLoan(newLoan);
	}


I want to be able to do something like this though...(this code does not work)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
 
// Read array from the file
	fstream binaryio; // Create stream object

	// Read loan back from the file
	binaryio.open(inputFilename, ios::in | ios::binary);


	binaryio.seekg (0, ios::end);
	int length = binaryio.tellg() / sizeof(int);
	binaryio.seekg(0); //to return the file pointer to the beginning
	Loan *newLoan;

	char *result = new char [length];

	// Display array
	for (int i = 0; i < length; i++)
	{
		// Reading one int at a time
		binaryio.read(reinterpret_cast<char*> (&newLoan[i]), sizeof(result[i]));
		if ( binaryio.eof() ) // Will check for end of file
			 break; // Exit from the while if end of file
		result[i] = newloan[i] + 5;
		// Then I will write result to another file
	}


Basically I want to retrieve the binary Loan objects that were stored in Exercise13_6.dat (which I can do). Then I want to store the objects in the result array.
naraku9333 (2163)
Doesnt look like your allocating any memory for newLoan. For result[i] = newloan[i] + 5; to work you will likely need to overload operator+
kraigballa (150)
How would I go about doing that for an object? I allocated memory for result...
naraku9333 (2163)
I allocated memory for result...
Yes, but newLoan doesnt point anywhere.
What does your Loan object look like?
kraigballa (150)
Here's the display from line 22 on the second piece of code:

1
2
3
4
5
6
 
void displayLoan(Loan &loan)
{
	cout << loan.getAnnualInterestRate() << " ";
	cout << loan.getNumberOfYears() << " ";
	cout << loan.getLoanAmount() << endl;
}
naraku9333 (2163)
Something like this maybe,
1
2
3
4
5
6
7
 
Loan Loan::operator+(const int num) const
{
    Loan tmp = *this;
    //then add to the val you want
    tmp.loanAmount += num;
    return tmp;
}

You'll also want to overload operator= something like...
1
2
3
4
5
6
7
8
9
 
Loan& Loan::operator=(const Loan& op2)
{
     if(this != &op2)
     {
          Loan tmp;
          //copy vars
          tmp->var = op2->var;//etc
     }
}


Obviously I dont know your variable names, but this should get you in the right direction.
Topic archived. No new replies allowed.