1 files changed, 166 insertions, 0 deletions
diff --git a/reference/C/CONTRIB/SNIP/drvalid.c b/reference/C/CONTRIB/SNIP/drvalid.c
new file mode 100755
index 0000000..de0204a
--- /dev/null
+++ b/reference/C/CONTRIB/SNIP/drvalid.c
@@ -0,0 +1,166 @@
+/*
+**  DRVALID.C - validate disk drives
+**
+**  Original Copyright 1988-1991 by Bob Stout as part of
+**  the MicroFirm Function Library (MFL)
+**
+**  This subset version is functionally identical to the
+**  version originally published by the author in Tech Specialist
+**  magazine and is hereby donated to the public domain.
+**
+**  Uses ABSDISKC.C and ABSDISK.ASM in SNIPPETS.
+*/
+
+#include <dos.h>
+#include <stdlib.h>
+
+typedef enum {ERROR = -1, SUCCESS, FALSE = 0, TRUE} LOGICAL;
+
+/*
+**  Function to read an absolute disk sector
+*/
+
+int AbsDiskRead(unsigned short, size_t, size_t, void *);
+
+/*
+**  getdrv()
+**
+**  Just as getcwd() returns the default directory, getdrv() returns
+**  the current drive.
+**
+**  Arguments: None.
+**
+**  Returns:   Current drive (0 = A:, 1 = B:, etc.)
+**
+**  Side effects: none
+*/
+
+int getdrv(void)
+{
+      union REGS regs;
+
+      regs.h.ah = 0x19;
+      intdos(&regs, &regs);
+      return (regs.h.al);
+}
+
+/*
+**  chdrv()
+**
+**  Like chdir(), except changes drives rather than directories.
+**
+**  Arguments: 1 - target drive (0 = A:, 1 = B:, etc.)
+**
+**  Returns: SUCCESS or ERROR
+**
+**  Side effects: none
+*/
+
+LOGICAL chdrv(int drive)
+{
+      union REGS regs;
+
+      regs.h.ah = 0x0e;
+      regs.h.dl = (char)drive;
+      intdos(&regs, &regs);
+      if (drive != getdrv())
+            return ERROR;
+      else  return SUCCESS;
+}
+
+/*
+**  drvalid()
+**
+**  Verifies whether a logical disk drive is available without
+**  triggering the DOS critical error handler.
+**
+**  Arguments: 1 - target drive (0 = A;, 1 = B:, etc.)
+**
+**  Returns:   TRUE  - drive is valid
+**             FALSE - drive is invalid
+**
+**  Side effects: none
+*/
+
+LOGICAL drvalid(int drive)
+{
+      int original, result;
+
+      original = getdrv();
+      result   = (SUCCESS == chdrv(drive));
+      chdrv(original);
+      return result;
+}
+
+/*
+**  drvrdy()
+**
+**  Checks whether a drive with removable media is ready.
+**
+**  Arguments: 1 - target drive (0 = A;, 1 = B:, etc.)
+**
+**  Returns:   TRUE  - drive is ready
+**             FALSE - drive is not ready
+**             ERROR - other read error
+**
+**  Side effects: none
+*/
+
+LOGICAL drvrdy(int drive)
+{
+      int status;
+      char buf[2048];         /* nice & roomy   */
+
+      status = AbsDiskRead(drive, 1, 0, buf);
+      if (0 == status)
+            return TRUE;
+      status &= 0xff;
+      if (2 == status)
+            return FALSE;
+      else  return ERROR;
+}
+
+#ifdef TEST
+
+#include <stdio.h>
+#include <ctype.h>
+
+int main(int argc, char *argv[])
+{
+      int drive;
+
+      if (2 > argc)
+      {
+            puts("Usage: DRVALID drive[:]");
+            return EXIT_FAILURE;
+      }
+      drive = toupper(*argv[1]);
+      if (!isalpha(drive))
+      {
+            puts("Error: Invalid drive name");
+            return EXIT_FAILURE;
+      }
+      printf("Drive %c: is %svalid\n", drive,
+            drvalid(drive - 'A') ? "" : "not ");
+      if (2 < _osmajor)
+      {
+            union REGS regs;
+
+            regs.x.ax = 0x4408;
+            regs.h.bl = (unsigned char)(drive - '@');
+            intdos(&regs, &regs);
+            printf("ioctl returned Cflag=%s\n",
+                  regs.x.cflag ? "TRUE" : "FALSE");
+            printf("ioctl returned AX=0x%X\n", regs.x.ax);
+            printf("Drive %c is%s removable\n", drive,
+                  regs.x.ax ? " not" : "");
+            if (0 == regs.x.ax)
+            {
+                  printf("Drive %c is %sready\n", drive,
+                        drvrdy(drive - 'A') ? "" : "not ");
+            }
+      }
+      return EXIT_SUCCESS;
+}
+
+#endif /* TEST */