NAME
XrmGetResource, XrmQGetResource, XrmQGetSearchList,
XrmQGetSearchResource - retrieve database resources and search lists
SYNTAX
Bool XrmGetResource(XrmDatabase database, char *str_name, char
*str_class, char **str_type_return, XrmValue *value_return);
Bool XrmQGetResource(XrmDatabase database, XrmNameList quark_name,
XrmClassList quark_class, XrmRepresentation *quark_type_return,
XrmValue *value_return);
typedef XrmHashTable *XrmSearchList;
Bool XrmQGetSearchList(XrmDatabase database, XrmNameList names,
XrmClassList classes, XrmSearchList list_return, int
list_length);
Bool XrmQGetSearchResource(XrmSearchList list, XrmName name, XrmClass
class, XrmRepresentation *type_return, XrmValue *value_return);
ARGUMENTS
class Specifies the resource class.
classes Specifies a list of resource classes.
database Specifies the database that is to be used.
list Specifies the search list returned by XrmQGetSearchList.
list_length
Specifies the number of entries (not the byte size) allocated
for list_return.
list_return
Returns a search list for further use.
name Specifies the resource name.
names Specifies a list of resource names.
quark_class
Specifies the fully qualified class of the value being
retrieved (as a quark).
quark_name
Specifies the fully qualified name of the value being
retrieved (as a quark).
quark_type_return
Returns the representation type of the destination (as a
quark).
str_class Specifies the fully qualified class of the value being
retrieved (as a string).
str_name Specifies the fully qualified name of the value being
retrieved (as a string).
str_type_return
Returns the representation type of the destination (as a
string).
type_return
Returns data representation type.
value_return
Returns the value in the database.
DESCRIPTION
The XrmGetResource and XrmQGetResource functions retrieve a resource
from the specified database. Both take a fully qualified name/class
pair, a destination resource representation, and the address of a value
(size/address pair). The value and returned type point into database
memory; therefore, you must not modify the data.
The database only frees or overwrites entries on XrmPutResource,
XrmQPutResource, or XrmMergeDatabases. A client that is not storing
new values into the database or is not merging the database should be
safe using the address passed back at any time until it exits. If a
resource was found, both XrmGetResource and XrmQGetResource return
True; otherwise, they return False.
The XrmQGetSearchList function takes a list of names and classes and
returns a list of database levels where a match might occur. The
returned list is in best-to-worst order and uses the same algorithm as
XrmGetResource for determining precedence. If list_return was large
enough for the search list, XrmQGetSearchList returns True; otherwise,
it returns False.
The size of the search list that the caller must allocate is dependent
upon the number of levels and wildcards in the resource specifiers that
are stored in the database. The worst case length is %3 sup n%, where
n is the number of name or class components in names or classes.
When using XrmQGetSearchList followed by multiple probes for resources
with a common name and class prefix, only the common prefix should be
specified in the name and class list to XrmQGetSearchList.
The XrmQGetSearchResource function searches the specified database
levels for the resource that is fully identified by the specified name
and class. The search stops with the first match.
XrmQGetSearchResource returns True if the resource was found;
otherwise, it returns False.
A call to XrmQGetSearchList with a name and class list containing all
but the last component of a resource name followed by a call to
XrmQGetSearchResource with the last component name and class returns
the same database entry as XrmGetResource and XrmQGetResource with the
fully qualified name and class.
MATCHING RULES
The algorithm for determining which resource database entry matches a
given query is the heart of the resource manager. All queries must
fully specify the name and class of the desired resource (use of the
characters ‘‘*’’ and ‘‘?’’ are not permitted). The library supports up
to 100 components in a full name or class. Resources are stored in the
database with only partially specified names and classes, using pattern
matching constructs. An asterisk (*) is a loose binding and is used to
represent any number of intervening components, including none. A
period (.) is a tight binding and is used to separate immediately
adjacent components. A question mark (?) is used to match any single
component name or class. A database entry cannot end in a loose
binding; the final component (which cannot be the character ‘‘?’’) must
be specified. The lookup algorithm searches the database for the entry
that most closely matches (is most specific for) the full name and
class being queried. When more than one database entry matches the
full name and class, precedence rules are used to select just one.
The full name and class are scanned from left to right (from highest
level in the hierarchy to lowest), one component at a time. At each
level, the corresponding component and/or binding of each matching
entry is determined, and these matching components and bindings are
compared according to precedence rules. Each of the rules is applied
at each level before moving to the next level, until a rule selects a
single entry over all others. The rules, in order of precedence, are:
1. An entry that contains a matching component (whether name, class,
or the character ‘‘?’’) takes precedence over entries that elide
the level (that is, entries that match the level in a loose
binding).
2. An entry with a matching name takes precedence over both entries
with a matching class and entries that match using the character
‘‘?’’. An entry with a matching class takes precedence over
entries that match using the character ‘‘?’’.
3. An entry preceded by a tight binding takes precedence over entries
preceded by a loose binding.
SEE ALSO
XrmInitialize(3), XrmMergeDatabases(3), XrmPutResource(3),
XrmUniqueQuark(3)
Xlib - C Language X Interface