Adding Parameters to a DPB

Sometimes it is useful to add parameters to an existing DPB at run time. For example, when an application runs, it might determine a user’s name and password and supply those values dynamically. The isc_expand_dpb() function can be used to pass the following additional parameters to a populated DPB at run time:

Table 4.4 DPB parameters recognized by isc_expand_dpb()

Parameter	Purpose
isc_dpb_user_name	String user name, up to 255 characters
isc_dpb_password	String password, up to 255 characters
isc_dpb_lc_messages	String specifying a language-specific message file
isc_dpb_lc_ctype	String specifying the character set to be used
isc_dpb_sql_role_name	String role name, up to 255 characters

Important: If you expect to add any of these parameters at run time, then create a larger than necessary DPB before calling isc_expand_dpb(), so that this function does not need to reallocate DPB storage space at run time. isc_expand_dbp() can reallocate space, but that space is not automatically freed when the database is detached.

isc_expand_dpb() requires the following parameters:

Table 4.5 isc_expand_dbp()parameters

Parameter	Type	Description
dpb	char**	Pointer to a DPB
dpb_size	unsigned short*	Pointer to the end of the currently used portion of the DPB
...	chart*	Pointers to item type and items to add to the DPB

The third parameter in the table, “…”, indicates a variable number of replaceable parameters. Each parameter is a character pointer with a unique name. The final parameter must be a NULL or a hexadecimal zero.

Important: isc_expand_dpb() allocates a new block for the DPB. To avoid memory leaks, call isc_free() to release that space.

The following code demonstrates how isc_expand_dpb() is called to add a user name and password to the DPB after they are elicited from a user at run time:

char dpb_buffer[256], *dpb, *p;

char uname[256], upass[256];

short dpb_length;

/* Construct a database parameter buffer. */

dpb = dpb_buffer;

*dpb++ = isc_dpb_version1;

*dpb++ = isc_dpb_num_buffers;

*dpb++ = 1;

*dpb++ = 90;

dpb_length = dpb - dpb_buffer;

dpb = dpb_buffer;

/* Now ask user for name and password. */

prompt_user("Enter your user name: ");

gets(uname);

prompt_user("\nEnter your password: ");

gets(upass);

/* Will string overflow buffer? */

if ((sizeof (dpb_buffer) - dpb_length) <= strlen (uname) + strlen (upass) +

sizeof (isc_dpb_user_name) + sizeof (isc_dpb_password)) {

/* Call expand_dpb) */

isc_expand_dpb(&dpb, &dpb_length, isc_dpb_user_name, uname,

isc_dpb_password, upass, NULL);

}

else

/* No, add parameters locally */

.....

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