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GConfValue
Datatype The GConfValue
struct represents
a value that can be obtained from or stored in the
configuration database. It is simply a type marker
and a union of several value types, with constructor,
destructor, "setter" and "getter" functions. When possible
the GConf library allows you to deal with simple C types
instead of a GConfValue
, but
sometimes there is simply no way to know the type of an
object in advance. The libgnome/gnome-config.h
interface simply returns strings in this case, for the
programmer to parse manually; this was phenomenally broken and
GConf fixes it with GConfValue
.
GConfValue
To read a GConfValue
, you first
determine its type and then read the value using one
of its accessor macros. The following useless code should
demonstrate this:
void print_value(GConfValue* value) { switch (value->type) { case GCONF_VALUE_STRING: printf("%s\n", gconf_value_get_string(value)); break; case GCONF_VALUE_INT: printf("%d\n", gconf_value_get_int(value)); break; case GCONF_VALUE_FLOAT: printf("%g\n", gconf_value_get_float(value)); break; case GCONF_VALUE_BOOL: printf("%s", gconf_value_get_bool(value) ? "true" : "false"); break; case GCONF_VALUE_SCHEMA: { GConfSchema* schema = gconf_value_get_schema(value); /* printing a schema would be complicated, you get the idea */ } break; case GCONF_VALUE_LIST: { GSList* iter = gconf_value_get_list(value); while (iter != NULL) { GConfValue* element = iter->data; print_value(element); iter = g_slist_next(iter); } } break; case GCONF_VALUE_PAIR: print_value(gconf_value_get_car(value)); print_value(gconf_value_get_cdr(value)); break; case GCONF_VALUE_INVALID: /* This is used internally by GConf, you can also use it yourself to indicate errors and such. It won't be returned from GConf functions though. */ printf("invalid value"); break; default: g_assert_not_reached(); break; } } |
A special note about values of type GCONF_VALUE_LIST:
the list contains GConfValue
objects, and all
objects in the list must have the same type. You can get the type of
the list with the gconf_value_get_list_type()
macro.
GConfValue
Often you obtain a GConfValue
from
a GConf routine such as gconf_engine_get ()
,
but you can also create them yourself with
gconf_value_new()
.
gconf_value_new()
takes a single
argument, the type of the newly-created value. Value types
can't be changed after creating the value.
You must initialize your values |
Newly-constructed values are invalid; if you use the accessor macros
before you set the contents of the value, the results are
undefined. Use |
You can destroy a GConfValue
with
gconf_value_free()
, and copy one
with gconf_value_copy()
. The copy is a
deep copy, that is, child values contained in lists or
pairs are also copied.