C++ Code to Access Linux Hard Disk Sectors (with a LoopBack Virtual Hard Disk)

[shen747]

Hi all,

I'm kind of new to programming in Linux & c/c++. I'm currently writing a FileManager using Ubuntu Linux(10.10) for Learning Purposes. I've got started on this project by creating a loopback device to be used as my virtual hard disk. After creating the loop back hard disk and mounting it has the following configuration.

$> sudo fdisk -l /dev/loop0

Disk /dev/loop0: 10 MB, 10977280 bytes
255 heads, 63 sectors/track, 1 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

Disk /dev/loop0 doesn't contain a valid partition table
 

Now what I want to do is develop a c++ program to read & write files to this loop back device,which I'm using to simulate an actual hard disk,at the blocks & sectors level. So far I've come up with the following code. But I'm still unable to read files from the hard disk one block at a time.

#include <iostream>
#include <stdio.h>

using namespace std;

int main()
{

    char block[512];
    int length=0;
    cout<<"Implementation of the File Handler Read Method..."<<endl;

    FILE *f = fopen("/dev/loop0", "r");
    if(f == NULL)
    {
        cout<<"Error In Opening the HardDisk File Retuning Error..."<<endl;
        return -1;
    }

    //Read One Block of Data to Buffer
    length = fread(block, 1, sizeof(block), f);

    /* Do something with the data */
    cout<<"Length : "<<length<<endl;

    return 0;
}

When I run this Program All what I get is the message for NULL.
"Error In Opening the HardDisk File Retuning Error...".
Could you please help me by pointing what am I doing wrong here ?. So I could open the loopback device as a file an access it at the sectors & block level.

[jsmith]

What is errno?