Function SetVariableHooks

src/bin/psql/variables.c:314–361

* Attach substitute and/or assign hook functions to the named variable. * If you need only one hook, pass NULL for the other. * * If the variable doesn't already exist, create it with value NULL, just so * we have a place to store the hook function(s). (The substitute hook might * immediately change the NULL to something else; if not, this state is * externally the same as the variable not

 * because this should get called before any user-supplied value is assigned.
 */
void
SetVariableHooks(VariableSpace space, const char *name,
				 VariableSubstituteHook shook,
				 VariableAssignHook ahook)
{
	struct _variable *current,
			   *previous;

	if (!space || !name)
		return;

	if (!valid_variable_name(name))
		return;

	for (previous = space, current = space->next;
		 current;
		 previous = current, current = current->next)
	{
		int			cmp = strcmp(current->name, name);

		if (cmp == 0)
		{
			/* found entry, so update */
			current->substitute_hook = shook;
			current->assign_hook = ahook;
			if (shook)
				current->value = (*shook) (current->value);
			if (ahook)
				(void) (*ahook) (current->value);
			return;
		}
		if (cmp > 0)
			break;				/* it's not there */
	}

	/* not present, make new entry */
	current = pg_malloc(sizeof *current);
	current->name = pg_strdup(name);
	current->value = NULL;
	current->substitute_hook = shook;
	current->assign_hook = ahook;
	current->next = previous->next;
	previous->next = current;
	if (shook)
		current->value = (*shook) (current->value);
	if (ahook)
		(void) (*ahook) (current->value);
}

/*
 * Return true iff the named variable has substitute and/or assign hook