Pointer variables

A pointer variable is a 4-byte pointer field containing an address. All HLL service routines require one pointer variable called Hlbptr. NetView® calculates the value of Hlbptr and passes it to the HLL command processor or installation exit. When Hlbptr is received as an initial parameter, do not assign a value to Hlbptr. This is the only parameter of this type that you do not have to assign.

Note: You do not need to specify the Hlbptr parameter when coding HLL service routine invocations in C. Hlbptr is inserted for you before the HLL service routine is started.

If an HLL service routine is expecting an address in a pointer field, you are responsible for assigning a value to that pointer field before starting the HLL service routine. For C, use the & (address) operator when passing pointer variables to HLL service routines rather than creating a separate pointer variable for this purpose. This ensures that the pointer variable is assigned a value before starting the HLL service routine.

Using Pointer Variables in C shows an example of using pointer variables in C. Some of the steps are explained in more detail following the figure.

Using Pointer Variables in C

 1   #define VARTOVAR   "VARTOVAR"    /* VARTOVAR constant             */
 2   Dsihlb *Hlbptr;                  /* HLB pointer MUST BE DEFINED   */
 3   Dsivarch *srcptr;                /* Pointer to source buffer      */
     Dsivarch *dstptr;                /* Pointer to destination buffer */

     int dstlen;                      /* Length of destination buffer  */

     Dsivarch srcbuf;                 /* Source buffer                 */
     Dsivarch dstbuf;                 /* Destination buffer            */

 4   srcptr = &srcbuf;                /* Address of source buffer      */
     dstptr = &dstbuf;                /* Address of destination buffer */

     dstlen = 255;

 5   Cnmcpys(srcptr,dstptr,dstlen,VARTOVAR);   /* Copy buffer          */

The descriptions for the steps shown in Using Pointer Variables in C are:

2: Hlbptr is defined as a pointer variable. You must not assign a value to Hlbptror include it in the Cnmcpys invocation. NetView inserts Hlbptr in the parameter list for you during the compilation's preprocessor phase.
3: srcptr is defined as a pointer to a structure of type Dsivarch (varying length character string).
4: srcptr is assigned the address of the source buffer (srcbuf) to be used as a operand to Cnmcpys
5: srcptr is passed as a parameter to Cnmcpys.
Using the & (address) operator in C eliminates the need to define pointer variables. Note the use of a string constant instead of the VARTOVAR constant in this example:

   Cnmcpys(&srcbuf,&dstbuf,dstlen,"VARTOVAR"); /* Copy buffer         */