How to "read" the MBR (Master Boot Record) in C?

Question

I just want to write a program to analyze MBR in C.

I've known some ways to read it through APIs on Windows or commands on Linux.

But, can I do it in C without any platform-dependent limitation?

If I can't, is there any reason?

Answer 1

Reading the master boot record is platform-dependent, the following code for instance works on Windows (if you have the privileges to do it)

#include <windows.h>
#include <stdio.h>
#include <iostream>
using namespace std;
short ReadSect
       (const char *_dsk,    // disk to access
       char *&_buff,         // buffer where sector will be stored
       unsigned int _nsect   // sector number, starting with 0
       )
{
  DWORD dwRead;   
  HANDLE hDisk=CreateFile(_dsk,GENERIC_READ,FILE_SHARE_VALID_FLAGS,0,OPEN_EXISTING,0,0);
  if(hDisk==INVALID_HANDLE_VALUE) // this may happen if another program is already reading from disk
    {  
       CloseHandle(hDisk);
       return 1;
    }
  SetFilePointer(hDisk,_nsect*512,0,FILE_BEGIN); // which sector to read

  ReadFile(hDisk,_buff,512,&dwRead,0);  // read sector
  CloseHandle(hDisk);
  return 0;
}

int main()
{
  char * drv="\\\\.\\C:"; 
  char *dsk="\\\\.\\PhysicalDrive0";
  int sector=0;

  char *buff=new char[512];
  ReadSect(dsk,buff,sector);
  if((unsigned char)buff[510]==0x55 && (unsigned char)buff[511]==0xaa) cout <<"Disk is bootable!"<<endl;


  getchar();

}

http://www.cplusplus.com/forum/windows/18019/

On Linux you can even use a terminal command

sudo dd if=/dev/sda ibs=512 count=1 | hexdump -C

Best solution would be to #ifdef your code and render it platform-dependent.