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CGETCAP(3) NetBSD Library Functions Manual CGETCAP(3)
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cgetent, cgetset, cgetmatch, cgetcap, cgetnum, cgetstr, cgetustr,
cgetfirst, cgetnext, cgetclose, cexpandtc -- capability database access
Standard C Library (libc, -lc)
cgetent(char **buf, const char * const *db_array, const char *name);
cgetset(const char *ent);
cgetmatch(const char *buf, const char *name);
cgetcap(char *buf, const char *cap, int type);
cgetnum(char *buf, const char *cap, long *num);
cgetstr(char *buf, const char *cap, char **str);
cgetustr(char *buf, const char *cap, char **str);
cgetfirst(char **buf, const char * const *db_array);
cgetnext(char **buf, const char * const *db_array);
cgetent() extracts the capability name from the database specified by the
NULL terminated file array db_array and returns a pointer to a
malloc(3)'d copy of it in buf. cgetent() will first look for files end-
ing in .db (see cap_mkdb(1)) before accessing the ASCII file.
buf must be retained through all subsequent calls to cgetmatch(),
cgetcap(), cgetnum(), cgetstr(), and cgetustr(), but may then be
On success 0 is returned, 1 if the returned record contains an unresolved
"tc" expansion, -1 if the requested record couldn't be found, -2 if a
system error was encountered (couldn't open/read a file, etc.) also set-
ting errno, and -3 if a potential reference loop is detected (see
"tc=name" comments below).
cgetset() enables the addition of a character buffer containing a single
capability record entry to the capability database. Conceptually, the
entry is added as the first ``file'' in the database, and is therefore
searched first on the call to cgetent(). The entry is passed in ent. If
ent is NULL, the current entry is removed from the database.
cgetset() must precede the database traversal. It must be called before
the cgetent() call. If a sequential access is being performed (see
below), it must be called before the first sequential access call
(cgetfirst() or cgetnext()), or be directly preceded by a cgetclose()
call. On success 0 is returned and -1 on failure.
cgetmatch() will return 0 if name is one of the names of the capability
record buf, -1 if not.
cgetcap() searches the capability record buf for the capability cap with
type type. A type is specified using any single character. If a colon
(`:') is used, an untyped capability will be searched for (see below for
explanation of types). A pointer to the value of cap in buf is returned
on success, NULL if the requested capability couldn't be found. The end
of the capability value is signaled by a `:' or ASCII NUL (see below for
capability database syntax).
cgetnum() retrieves the value of the numeric capability cap from the
capability record pointed to by buf. The numeric value is returned in
the long pointed to by num. 0 is returned on success, -1 if the
requested numeric capability couldn't be found.
cgetstr() retrieves the value of the string capability cap from the capa-
bility record pointed to by buf. A pointer to a decoded, NUL terminated,
malloc(3)'d copy of the string is returned in the char * pointed to by
str. The number of characters in the decoded string not including the
trailing NUL is returned on success, -1 if the requested string capabil-
ity couldn't be found, -2 if a system error was encountered (storage
cgetustr() is identical to cgetstr() except that it does not expand spe-
cial characters, but rather returns each character of the capability
cgetfirst(), cgetnext(), comprise a function group that provides for
sequential access of the NULL pointer terminated array of file names,
db_array. cgetfirst() returns the first record in the database and
resets the access to the first record. cgetnext() returns the next
record in the database with respect to the record returned by the previ-
ous cgetfirst() or cgetnext() call. If there is no such previous call,
the first record in the database is returned. Each record is returned in
a malloc(3)'d copy pointed to by buf. "tc" expansion is done (see
"tc=name" comments below).
Upon completion of the database 0 is returned, 1 is returned upon suc-
cessful return of record with possibly more remaining (we haven't reached
the end of the database yet), 2 is returned if the record contains an
unresolved "tc" expansion, -1 is returned if an system error occurred,
and -2 is returned if a potential reference loop is detected (see
"tc=name" comments below). Upon completion of database (0 return) the
database is closed.
cgetclose() closes the sequential access and frees any memory and file
descriptors being used. Note that it does not erase the buffer pushed by
a call to cgetset().
CAPABILITY DATABASE SYNTAX
Capability databases are normally ASCII and may be edited with standard
text editors. Blank lines and lines beginning with a `#' are comments
and are ignored. Lines ending with a `\' indicate that the next line is
a continuation of the current line; the `\' and following newline are
ignored. Long lines are usually continued onto several physical lines by
ending each line except the last with a `\'.
Capability databases consist of a series of records, one per logical
line. Each record contains a variable number of `:'-separated fields
(capabilities). Empty fields consisting entirely of white space charac-
ters (spaces and tabs) are ignored.
The first capability of each record specifies its names, separated by `|'
characters. These names are used to reference records in the database.
By convention, the last name is usually a comment and is not intended as
a lookup tag. For example, the vt100 record from the termcap database
giving four names that can be used to access the record.
The remaining non-empty capabilities describe a set of (name, value)
bindings, consisting of a name optionally followed by a typed value:
name typeless [boolean] capability name is present [true]
nameTvalue capability (name, T) has value value
name@ no capability name exists
nameT@ capability (name, T) does not exist
Names consist of one or more characters. Names may contain any character
except `:', but it's usually best to restrict them to the printable char-
acters and avoid use of graphics like `#', `=', `%', `@', etc.
Types are single characters used to separate capability names from their
associated typed values. Types may be any character except a `:'. Typi-
cally, graphics like `#', `=', `%', etc. are used. Values may be any
number of characters and may contain any character except `:'.
CAPABILITY DATABASE SEMANTICS
Capability records describe a set of (name, value) bindings. Names may
have multiple values bound to them. Different values for a name are dis-
tinguished by their types. cgetcap() will return a pointer to a value of
a name given the capability name and the type of the value.
The types `#' and `=' are conventionally used to denote numeric and
string typed values, but no restriction on those types is enforced. The
functions cgetnum() and cgetstr() can be used to implement the tradi-
tional syntax and semantics of `#' and `='. Typeless capabilities are
typically used to denote boolean objects with presence or absence indi-
cating truth and false values respectively. This interpretation is con-
veniently represented by:
(getcap(buf, name, ':') != NULL)
A special capability, "tc=name", is used to indicate that the record
specified by name should be substituted for the "tc" capability. "tc"
capabilities may interpolate records which also contain "tc" capabilities
and more than one "tc" capability may be used in a record. A "tc" expan-
sion scope (i.e. where the argument is searched for) contains the file in
which the "tc" is declared and all subsequent files in the file array.
csetexpandtc() can be used to control if "tc" expansion is performed or
When a database is searched for a capability record, the first matching
record in the search is returned. When a record is scanned for a capa-
bility, the first matching capability is returned; the capability
":nameT@:" will hide any following definition of a value of type T for
name; and the capability ":name@:" will prevent any following values of
name from being seen.
These features combined with "tc" capabilities can be used to generate
variations of other databases and records by either adding new capabili-
ties, overriding definitions with new definitions, or hiding following
definitions via `@' capabilities.
example|an example of binding multiple values to names:\
The capability foo has two values bound to it (bar of type `%' and blah
of type `^') and any other value bindings are hidden. The capability abc
also has two values bound but only a value of type `$' is prevented from
being defined in the capability record more.
new|new_record|a modification of "old":\
old|old_record|an old database record:\
The records are extracted by calling cgetent() with file1 preceding
file2. In the capability record new in file1, "fript=bar" overrides the
definition of "fript=foo" interpolated from the capability record old in
file2, "who-cares@" prevents the definition of any who-cares definitions
in old from being seen, "glork#200" is inherited from old, and blah and
anything defined by the record extensions is added to those definitions
in old. Note that the position of the "fript=bar" and "who-cares@" defi-
nitions before "tc=old" is important here. If they were after, the defi-
nitions in old would take precedence.
CGETNUM AND CGETSTR SYNTAX AND SEMANTICS
Two types are predefined by cgetnum() and cgetstr():
name#number numeric capability name has value number
name=string string capability name has value string
name#@ the numeric capability name does not exist
name=@ the string capability name does not exist
Numeric capability values may be given in one of three numeric bases. If
the number starts with either `0x' or `0X' it is interpreted as a hexa-
decimal number (both upper and lower case a-f may be used to denote the
extended hexadecimal digits). Otherwise, if the number starts with a `0'
it is interpreted as an octal number. Otherwise the number is inter-
preted as a decimal number.
String capability values may contain any character. Non-printable ASCII
codes, new lines, and colons may be conveniently represented by the use
of escape sequences:
^X ('X' & 037) control-X
\b, \B (ASCII 010) backspace
\t, \T (ASCII 011) tab
\n, \N (ASCII 012) line feed (newline)
\f, \F (ASCII 014) form feed
\r, \R (ASCII 015) carriage return
\e, \E (ASCII 027) escape
\c, \C (:) colon
\\ (\) back slash
\^ (^) caret
\nnn (ASCII octal nnn)
A `\' followed by up to three octal digits directly specifies the numeric
code for a character. The use of ASCII NULs, while easily encoded,
causes all sorts of problems and must be used with care since NULs are
typically used to denote the end of strings; many applications use `\200'
to represent a NUL.
cgetent(), cgetset(), cgetmatch(), cgetnum(), cgetstr(), cgetustr(),
cgetfirst(), and cgetnext() return a value greater than or equal to 0 on
success and a value less than 0 on failure. cgetcap() returns a charac-
ter pointer on success and a NULL on failure.
cgetclose(), cgetent(), cgetfirst(), and cgetnext() may fail and set
errno for any of the errors specified for the library functions:
fopen(3), fclose(3), open(2), and close(2).
cgetent(), cgetset(), cgetstr(), and cgetustr() may fail and set errno as
[ENOMEM] No memory to allocate.
Colons (`:') can't be used in names, types, or values.
There are no checks for "tc=name" loops in cgetent().
The buffer added to the database by a call to cgetset() is not unique to
the database but is rather prepended to any database used.
NetBSD 5.0 February 1, 2008 NetBSD 5.0