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Opens a virtual device driver (VDD), and returns a handle for it.


DosOpenVDD(pszVDD, phvdd)


pszVDD (PSZ) - input 
The ASCIIZ name of the virtual device driver to be opened.
phvdd (PHVDD) - output 
A pointer to the HVDD in which the handle of the virtual device driver is returned.

Return Code

ulrc (APIRET) - returns
DosOpenVDD returns one of the following values:
  • 0 NO_ERROR


DosOpenVDD opens a virtual device driver, and returns a handle for it.

If pszVDD specifies the name of an OS/2 virtual device driver, the returned handle allows an OS/2 protected-mode application to communicate with a virtual device driver by issuing DosRequestVDD.

Issue DosCloseVDD to close the handle of the virtual device driver.

Example Code

The following is NOT a complete C program. It is simply intended to provide an idea of how a protected-mode OS/2 process can communicate with a virtual device driver (VDD).

This example shows a protected-mode process calling a hypothetical VDD with a request to read a string of bytes from the VDD. Assume that the session identifier of the specified DOS session has been placed into SessionID already and that the sample virtual device driver has registered the name "VDD007" with the operating system.

 #define INCL_DOSMVDM     /* Multiple DOS sessions values */
 #define INCL_DOSERRORS   /* DOS Error values */
 #include <os2.h>
 #include <stdio.h>

 UCHAR   VDDName[10] = "VDD007";    /* Name of VDD */
 HVDD    VDDHandle   = NULLHANDLE;  /* Handle of VDD */
 SGID    SessionID   = 0;        /* Session identifier (should be initialized */
 ULONG   Command     = 3;        /* VDD function code (hypothetical) */
 APIRET  rc          = NO_ERROR;    /* Return code */
 UCHAR   InputBuffer[30]  = "Your command here";  /* Command information    */
 UCHAR   OutputBuffer[30] = "";                   /* Output data (returned) */

    rc = DosOpenVDD(VDDName, &VDDHandle);
    if (rc != NO_ERROR) {
       printf("VDD %s was not found.\n", rc);
       return 1;

    rc = DosRequestVDD(VDDHandle,              /* Handle of VDD */
                       SessionID,              /* Session ID */
                       Command,                /* Command to send to VDD */
                       sizeof(InputBuffer),    /* Length of input */
                       InputBuffer,            /* Input buffer */
                       sizeof(OutputBuffer),   /* Length of output area */
                       OutputBuffer);          /* Output from command */
    if (rc != NO_ERROR) {
        printf("DosRequestVDD error: return code = %u\n", rc);
        return 1;

    rc = DosCloseVDD(VDDHandle);               /* Close the VDD */
    if (rc != NO_ERROR) {
        printf("DosCloseVDD error: return code = %u\n", rc);
        return 1;

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