How to read/write sets of orderded numbers in binary

[vermarajeev]

The easiest would be to store the dimensions to expect first, for example, this matrix:

1 1 1
2 2 2
3 3 3

Would be stored as

3 3 1 1 1 2 2 2 3 3 3

Where the first two threes would indicate that we're dealing with a 3x3 matrix. Then the data follow. Using an index, starting at 0 for the first one, then increasing you can find your matrix coordinate like this:

row = index/width; // Integer division, always rounds down
col = index%width; // Modulus

The final check would be to ensure that the index == width*height when you have reached the end of the file.

Also, when storing binary data using Qt, make sure to set your QDataStream version using myDataStreamObject->setVersion( xxx ); to ensure compatibility between Qt versions.

Hi e8johan,
I have written a sample program about what you have told in above post. Please correct me if I'm wrong...

#include <iostream>
#include <fstream>
using namespace std;
 
int main()
{
	int arr[3][3] = { 1, 1, 1,
					  2, 2, 2,
					  3, 3, 3 };
 
 
	ofstream ofs("test.txt", ios::binary);	
	const char* data = "33111222333";	
	string line = data;
	ofs.write( line.data(), line.length() );	
	ofs.close();
 
	char buffer[256];
	ifstream ifs("test.txt", ios::binary);
	ifs.getline(buffer, sizeof(buffer) );		
	ifs.close();
 
	string bufferdata = buffer;
 
	int width = bufferdata.at(0) - '0';
	int height = bufferdata.at(1) - '0';
 
	int index = 0;
	int row = 0, col = 0;
 
	while(1)
	{
		if( index == width*height )
			break;
 
	    row = index/width; // Integer division, always rounds down
		col = index%width; // Modulus
 
		cout<<"Row:"<<row<<" "<<"Col:"<<col<<endl;
                    bufferdata.at(index++);	
	}
	return 0;
}

#include <iostream>
#include <fstream>
using namespace std;

int main()
{
	int arr[3][3] = { 1, 1, 1,
					  2, 2, 2,
					  3, 3, 3 };

	
	ofstream ofs("test.txt", ios::binary);	
	const char* data = "33111222333";	
	string line = data;
	ofs.write( line.data(), line.length() );	
	ofs.close();
	
	char buffer[256];
	ifstream ifs("test.txt", ios::binary);
	ifs.getline(buffer, sizeof(buffer) );		
	ifs.close();

	string bufferdata = buffer;

	int width = bufferdata.at(0) - '0';
	int height = bufferdata.at(1) - '0';
	
	int index = 0;
	int row = 0, col = 0;
	
	while(1)
	{
		if( index == width*height )
			break;

	    row = index/width; // Integer division, always rounds down
		col = index%width; // Modulus

		cout<<"Row:"<<row<<" "<<"Col:"<<col<<endl;
                    bufferdata.at(index++);	
	}
	return 0;
}

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