Extract logical drives in system and select desired subset from them

#if !defined(__DEVTAB_I)
#define __DEVTAB_I
#include <windows.h> // For GetDriveTypeA()
#include <dos.h>
// It's a personal quirk - My private includes are all .i rather than .h
#include "initarr.i" // initialize array (name,#elements,value)
#include "curdrvs.i" // List of current drives from GetLogicalDrives()
                     // This routine is included here at the bottom
#include "diskdata.i"// getdfree() + enhancements (used for bytes/sector)

// Minimum call to devtab fills drive numbers (0-25) and types (1-4)
// Call may be made with 3, 4 or 5 arguments
// network/local status and removability can be requested
int devtab(int type,int dskid[],int drtyp[],int drnet[]);
int devtab(int type,int dskid[],int drtyp[]);

// The base routine assumes all 4 types of info requested
// dskid values are 0-25, drtyp values are 1-4,
// drnet values are 0/1,  drrmv values are 0/1
int devtab(int type,int dskid[],int drtyp[],int drnet[],int drrmv[])
{
// Return types from GetDriveTypeA()
const int Unknown     = 0;
const int NoRootDrive = 1;
const int Removable   = 2; 
const int LocalDisk   = 3; 
const int Network     = 4; 
const int CDrom       = 5; 
const int RAMDrive    = 6;
// Windows.h Drive Type Defines
// #define DRIVE_UNKNOWN     0
// #define DRIVE_NO_ROOT_DIR 1
// #define DRIVE_REMOVABLE   2
// #define DRIVE_FIXED       3
// #define DRIVE_REMOTE      4
// #define DRIVE_CDROM       5
// #define DRIVE_RAMDISK     6

// My drive type designations
const int Floppy      = 1;
const int Disk        = 2;
const int Cd          = 3;
const int Usb         = 4; // Non-floppy removable disks = USB

int i,j,k;
int numdisk;
int bs;
char drv[27];
int typ;
char drive[4]="?:\\"; // Data format for call to GetDriveInfoA

int FLOP=1,DISK=2,CD=4,USB=8,ALL=16,REMOVABLE=32,LOCAL=64,NETWORK=128;
// Calls here are in the form: drvcnt = devtab(LOCAL|DISK,a,b,c,d)
//                                    = devtab(NETWORK|CD, ......
//                                    = devtab(CD|USB|FLOP, ......

// Set drives to ALL if no drive specifcation (type = 0)
typ = type;
typ = typ & (NETWORK-1); 
typ = typ & (LOCAL-1);
if (typ == 0)
   type = type | ALL;

// If neither LOCAL nor NETWORK specified, default to both
if ((type & NETWORK) != NETWORK && (type & LOCAL) != LOCAL)
   {
   type = type | NETWORK;
   type = type | LOCAL;
   }

initarr(dskid,26,0);
initarr(drtyp,26,0);
initarr(drnet,26,0);
initarr(drrmv,26,0);

// Retrieve a list of drive letters in the system
// Fill all available drive data
// Next step filters from these what the caller wants to see
numdisk = getdrv(drv);

for (i=0; i<numdisk; i++)
   {
   dskid[i] = drv[i]-'A'; // Just return drive number, not letter
   drive[0] = drv[i];
   drrmv[i] = 0;
   drnet[i] = 0;
   k = GetDriveTypeA(drive);
   if (k == DRIVE_FIXED)
      drtyp[i] = Disk;
   else
   if (k == DRIVE_REMOTE)
      {
      drtyp[i] = Disk; // Assume disk
      drnet[i] = 1;
      getdiskdata(drv[i]-'A'+1,NULL,NULL,NULL,&bs); // Get bytes/sector
      // Network attached CDs show up as Disks according to GetDriveTypeA
      if (bs != 512) // Disks are 512 bytes/sector.
         drtyp[i] = Cd; 
      // Could also call GetVolumeInformationA() and check filesystem
      }
   else
   if (k == DRIVE_CDROM)
      drtyp[i] = Cd;
   else
   if (k == DRIVE_REMOVABLE)
      {
      if (i > 1)
         drtyp[i] = Usb;
      else
         drtyp[i] = Floppy;
      drrmv[i] = 1;
      }
         
   }
// Select the drives matching the caller's criteria
j = -1;
for (i=0; i<numdisk; i++)
   {
   // Get a match on device type
   if (
      ((type & ALL) == ALL ||
      (type & FLOP) ==  FLOP && drtyp[i]  == Floppy ||
      (type & DISK) ==  DISK && drtyp[i]  == Disk ||
      (type & CD) ==  CD && drtyp[i]  == Cd ||
      (type & USB) == USB && drtyp[i] == Usb ||
      (type & REMOVABLE) == REMOVABLE && drrmv[i])
      &&
      ((type & NETWORK) == NETWORK && drnet[i] ||
       (type & LOCAL) == LOCAL && !drnet[i])
      )
      {
      j++;
      dskid[j] = dskid[i];
      drtyp[j] = drtyp[i];
      drnet[j] = drnet[i];
      drrmv[j] = drrmv[i];
      }
   }
return j+1; // actual number of drives being returned
}
// User doesn't want removable status, make call using dummy remove array
int devtab(int type,int diskno[],int drtype[],int remote[])
{
int remove[26]; // dummy so far as caller is concerned
return(devtab(type,diskno,drtype,remote,remove));
}
// User only wants drive numbers and types. Make full call with dummy arrays
int devtab(int type,int diskno[],int drtype[])
{
int remote[26]; // dummy
int remove[26]; // dummy
return(devtab(type,diskno,drtype,remote,remove));
}
#endif

// Here's the routine that gets the list of logical drives
#if !defined(__GETDRV_I)
#define __GETDRV_I
#include <direct.h>
#include <dos.h>
#include <windows.h> // For GetLogicalDrives()
// Take advantage of overloading to allow calls with different data types
// to routines with the same names.
int getdrv(int drv[]); // INT  prototype
int getdrv(char drv[]);// CHAR prototype

int getdrv(int drv[]) // Fill int array with drive letters (0-25 +'A')
{
int drvs = GetLogicalDrives();
// low order bit on = drive A present, etc.
// 1101 = Drives D:, C: and A:, no B: drive.
// DCBA
int i,j,k;


i=-1; // drive #
j=-1; // array index
while(drvs)
   {
   i++;
   if (drvs & 1)
      {
      j++;
      drv[j] = i+'A';
      }
   drvs >>=1;
   }
return j+1;
}
int getdrv(char drv[]) // Fill string with drive letters
{
int drvs = GetLogicalDrives();
int i,j;


i=-1;
j=-1;
while(drvs)
   {
   i++;
   if (drvs & 1)
      {
      j++;
      drv[j] = i+'A';
      }
   drvs >>=1;
   }
drv[j+1] = '\0'; // Terminate string
return j+1;
}
#endif