Set the data pointer

The following code fragment creates an empty varying-length structure, which is a varying-length structure that has no data portion allocated:

#define VAR_MEM_SIZE 20
...
mi_lvarchar *new_lvarch;
char *var_text;
mi_integer var_len;
...
/* Allocate PER_COMMAND memory for varying-length data */
var_text = (char *)mi_dalloc(VAR_MEM_SIZE, PER_COMMAND);

/* Allocate an empty varying-length structure */
(void)mi_switch_mem_duration(PER_COMMAND);
new_lvarch = mi_new_var(0);

/* Store the varying-length data in the var_text buffer
 * with the fill_buffer() function (which you have coded). 
 * This function returns the actual length of the nonnull- 
 * terminated string. It does NOT put a null terminator at 
 * the end of the data.
 */
var_len = fill_buffer(var_text);

The following figure shows the format of the varying-length structure that new_lvarch references after the fill_buffer() function successfully completes.

The varying-length structure in Empty varying-length structure is empty because it has the following characteristics:

• Data length of zero
• NULL-valued pointer as its data pointer

After you have an empty varying-length structure, you can use the mi_set_varptr() function to set the data pointer to the PER_COMMAND memory duration, as the following code fragment shows:

/* Set the length of the new varying-length data */
mi_set_varlen(new_lvarch, VAR_MEM_SIZE);

/* Set the pointer to the data portion of the
 * varying-length structure to the PER_COMMAND memory
 * that 'var_text' references.
 */
mi_set_varptr(new_lvarch, var_text);

The preceding call to mi_set_varlen() updates the length in the varying-length structure to the length of 20 bytes. The following figure shows the format of the varying-length structure that new_lvarch references after the preceding call to mi_set_varptr() successfully completes.