===========================================================================
 BBS: The Abacus * HST/DS * Potterville MI
Date: 03-29-93 (20:48)             Number: 75
From: MARK CORGAN                  Refer#: 189
  To: DALE DAVIS                    Recvd: NO  
Subj: Write Protected Disks          Conf: (36) C Language
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Hello Dale!

25 Mar 93, Dale Davis writes to All:

 DD> Does anyone have any clues as to how I can check a disk to determine if it
 DD> is write protected before I write to it.  I'm writing a DOS program, and
 DD> I've tried a couple different things, but I keep crashing the program and
 DD> getting the DOS write-proteced disk error.  I know the answer is probobly
 DD> real obvious and located on page 1 of every C book I own, but if anyone
 DD> out there is really bored and can clue me in, I'd really appreciate it!

Try out this code. It is for drive A: but you should be able to follow it enough
 to test for drive C:.


#include <stdio.h>
#include <dos.h>
#include <stdlib.h>

#define RETURN_OK               0
#define RETURN_WRITE_PROTECT    1
#define RETURN_OTHER            2

char far buffer[10000];
char far *pbuf = buffer;

void main(void)
{
    union REGS      inregs, outregs;
    struct SREGS    segregs;
    int             retries = 0;
    int             rc = RETURN_OK;

    // Read logical sector 1
    inregs.h.ah = 0x00;             // Just clear it out
    inregs.h.al = 0x00;             // Disk drive A:
    inregs.x.cx = 0x01;             // Number of sectors to read
    inregs.x.dx = 0x01;             // Logical sector 1 (FAT)
    inregs.x.bx = FP_OFF(pbuf);     // Offset of buffer
    segregs.ds  = FP_SEG(pbuf);     // Segment address of buffer
    int86x(0x25, &inregs, &outregs, &segregs);

    // If the carry flag is set, then there was an error
    if (outregs.x.cflag) {
        rc = RETURN_OTHER;
    } else {
 // Write logical sector 1
 inregs.h.ah = 0x00;           // Just clear it out
 inregs.h.al = 0x00;           // Disk drive A:
 inregs.x.cx = 0x01;           // Number of sectors to write
 inregs.x.dx = 0x01;           // Logical sector 1 (FAT)
 inregs.x.bx = FP_OFF(pbuf);   // Offset of buffer
 segregs.ds  = FP_SEG(pbuf);   // Segment address of buffer
 int86x(0x26, &inregs, &outregs, &segregs);

 // If the carry flag is set, then there was an error
 if (outregs.x.cflag) {
     // If ah = 3 then there was a write protect error
     if (outregs.h.ah == 3) {
  rc = RETURN_WRITE_PROTECT;
     } else {
  rc = RETURN_OTHER;
     }
 }
    }
    exit(rc);
}



Mark

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