cgetent
, cgetset
,
cgetmatch
, cgetcap
,
cgetnum
, cgetstr
,
cgetustr
, cgetfirst
,
cgetnext
, cgetclose
—
capability database access routines
Standard C Library (libc, -lc)
#include <stdlib.h>
int
cgetent
(char
**buf, char
**db_array, const char
*name);
int
cgetset
(const
char *ent);
int
cgetmatch
(const
char *buf, const char
*name);
char *
cgetcap
(char
*buf, const char
*cap, int
type);
int
cgetnum
(char
*buf, const char
*cap, long
*num);
int
cgetstr
(char
*buf, const char
*cap, char
**str);
int
cgetustr
(char
*buf, const char
*cap, char
**str);
int
cgetfirst
(char
**buf, char
**db_array);
int
cgetnext
(char
**buf, char
**db_array);
int
cgetclose
(void);
The cgetent
() function 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. The cgetent
()
function will first look for files ending in .db (see
cap_mkdb(1))
before accessing the ASCII file. The buf argument must
be retained through all subsequent calls to
cgetmatch
(), cgetcap
(),
cgetnum
(), cgetstr
(), and
cgetustr
(), but may then be
free(3)'d.
On success 0 is returned, 1 if the returned record contains an unresolved
tc
expansion, -1 if the requested record could not be
found, -2 if a system error was encountered (could not open/read a file, etc.)
also setting errno, and -3 if a potential reference loop
is detected (see tc=
comments below).
The cgetset
() function 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. A call to 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.
The cgetmatch
() function will return 0 if
name is one of the names of the capability record
buf, -1 if not.
The cgetcap
() function 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 could not
be found. The end of the capability value is signaled by a `:' or ASCII
NUL
(see below for capability database syntax).
The cgetnum
() function 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 could not be found.
The cgetstr
() function retrieves the value
of the string capability cap from the capability
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 capability could not be found, -2 if a
system error was encountered (storage allocation failure).
The cgetustr
() function is identical to
cgetstr
() except that it does not expand special
characters, but rather returns each character of the capability string
literally.
The cgetfirst
() and
cgetnext
() functions comprise a function group that
provides for sequential access of the NULL
pointer
terminated array of file names, db_array. The
cgetfirst
() function returns the first record in the
database and resets the access to the first record. The
cgetnext
() function returns the next record in the
database with respect to the record returned by the previous
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=
comments below). Upon
completion of the database 0 is returned, 1 is returned upon successful
return of record with possibly more remaining (we have not reached the end
of the database yet), 2 is returned if the record contains an unresolved
tc
expansion, -1 is returned if a system error
occurred, and -2 is returned if a potential reference loop is detected (see
tc=
comments below). Upon completion of database (0
return) the database is closed.
The cgetclose
() function 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 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 characters
(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(5)
database begins:
d0|vt100|vt100-am|vt100am|dec
vt100:
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 names 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 is usually best to restrict them to the
printable characters 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 `:'. Typically,
graphics like `#', `=', `%', etc. are used. Values may be any number of
characters and may contain any character except `:'.
Capability records describe a set of (name, value) bindings. Names may have
multiple values bound to them. Different values for a name are distinguished
by their types. The cgetcap
()
function 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 traditional
syntax and semantics of `#' and `='. Typeless capabilities are typically
used to denote boolean objects with presence or absence indicating truth and
false values respectively. This interpretation is conveniently 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
expansion 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.
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
capability, 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 capabilities, overriding definitions with new
definitions, or hiding following definitions via `@' capabilities.
example|an example of binding multiple values to names:\
:foo%bar:foo^blah:foo@:\
:abc%xyz:abc^frap:abc$@:\
:tc=more:
The capability foo has two values bound to it (bar of type `%' and
blah of type `^') and any other value bindings are hidden. The capability
abc also has two values bound but only a value of type `$' is prevented from
being defined in the capability record more.
file1:
new|new_record|a modification of "old":\
:fript=bar:who-cares@:tc=old:blah:tc=extensions:
file2:
old|old_record|an old database record:\
:fript=foo:who-cares:glork#200:
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@ definitions before tc=old is important here. If
they were after, the definitions in old would take precedence.
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
hexadecimal 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 interpreted 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 `\' may be followed by up to three octal digits directly
specifies the numeric code for a character. The use of ASCII
NUL
s, while easily encoded, causes all sorts of
problems and must be used with care since NUL
s are
typically used to denote the end of strings; many applications use `\200' to
represent a NUL
.
The cgetent
(), cgetset
(),
cgetmatch
(), cgetnum
(),
cgetstr
(), cgetustr
(),
cgetfirst
(), and cgetnext
()
functions return a value greater than or equal to 0 on success and a value
less than 0 on failure. The cgetcap
() function returns
a character pointer on success and a NULL
on failure.
The cgetent
(), and
cgetset
() functions may fail and set
errno for any of the errors specified for the library
functions:
fopen(3),
fclose(3),
open(2),
and
close(2).
The cgetent
(),
cgetset
(), cgetstr
(), and
cgetustr
() functions may fail and set
errno as follows:
- [
ENOMEM
]
- No memory to allocate.
Colons (`:') cannot 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.