Referencing pointer host variables in C programs

If you use the Db2 coprocessor, you can reference any declared pointer host variables in your SQL statements.

Procedure

To reference pointer host variables in C and C++ programs:

Specify the pointer host variable exactly as it was declared.

The only exception is when you reference pointers to nul-terminated character arrays. In this case, you do not have to include the parentheses that were part of the declaration.

Examples

Examples: Scalar pointer host variable references

Table 1. Example references to scalar pointer host variables
Declaration	Description	Reference
`short *hvshortp;`	hvshortp is a pointer host variable that points to two bytes of storage.	`EXEC SQL set:*hvshortp=123;`
`double *hvdoubp;`	hvdoubp is a pointer host variable that points to eight bytes of storage.	`EXEC SQL set:*hvdoubp=456;`
`char (*hvcharpn) [20];`	hvcharpn is a pointer host variable that points to a nul-terminated character array of up to 20 bytes.	`EXEC SQL set: *hvcharpn='nul_terminated';`

Example:Bounded character pointer host variable reference

Suppose that your program declares the following bounded character pointer host variable:

struct {
  unsigned long len;
  char * data;
  } hvbcharp;

The following example references this bounded character pointer host variable:

hvcharp.len = dynlen;  a 
hvcharp.data = (char *) malloc (hvcharp.len);  b 
EXEC SQL set :hvcharp = 'data buffer with length';  c

Note:

a: dynlen can be either a compile time constant or a variable with a value that is assigned at run time.
b: Storage is dynamically allocated for hvcharp.data.
c: The SQL statement references the name of the structure, not an element within the structure.

Examples: Array pointer host variable references

Table 2. Example references to array pointer host variables
Declaration	Description	Reference
`short * hvarrpl[6]`	hvarrp1 is an array of 6 pointers that point to two bytes of storage each.	`EXEC SQL set:*hvarrpl[n]=123;`
`double * hvarrp2[3]`	hvarrp2 is an array of 3 pointers that point to 8 bytes of storage each.	`EXEC SQL set:*hvarrp2[n]=456;`
`struct { unsigned long len; char * data; } hvbarrp3[5];`	hvbarrp3 is an array of 5 bounded character pointers.	`EXEC SQL set :hvarrp3[n] = 'data buffer with length'`

Example: Structure array host variable reference

Suppose that your program declares the following pointer to the structure tbl_struct:

struct tbl_struct *ptr_tbl_struct =
 (struct tbl_struct *) malloc (sizeof (struct tbl_struct) * n);

To reference this data is SQL statements, use the pointer as shown in the following example. Assume that tbl_sel_cur is a declared cursor.

for (L_col_cnt = 0; L_col_cnt < n; L_con_cnt++)
{ ...
  EXEC SQL FETCH tbl_sel_cur INTO :ptr_tbl_struct [L_col_cnt]
  ...
}