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.

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 invoking 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 invoking the HLL service routine.

Figure 43 shows an example of using pointer variables in C. Some of the steps are explained in more detail following the figure.

 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 Figure 43 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         */

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