PC Extra Super CD 1998 January/PCPLUS131.iso/DJGPP/V2/DJLSR201.ZIP/src/libc/posix/regex/regex.txh

Text File | 1996-04-27 | 22.2 KB | 552 lines

@node regcomp, string
@subheading Syntax

@example
#include <sys/types.h>
#include <regex.h>

int regcomp(regex_t *preg, const char *pattern, int cflags);
@end example

@subheading Description

This function is part of the implementation of POSIX 1003.2 regular
expressions (@dfn{RE}s).

@code{regcomp} compiles the regular expression contained in the
@var{pattern} string, subject to the flags in @var{cflags}, and places
the results in the @code{regex_t} structure pointed to by @var{preg}.
(The regular expression syntax, as defined by POSIX 1003.2, is described
below.)

The parameter @var{cflags} is the bitwise OR of zero or more of the
following flags:

@table @code

@item REG_EXTENDED

Compile modern (@dfn{extended}) REs, rather than the obsolete
(@dfn{basic}) REs that are the default.

@item REG_BASIC

This is a synonym for 0, provided as a counterpart to
@code{REG_EXTENDED} to improve readability.

@item REG_NOSPEC

Compile with recognition of all special characters turned off.  All
characters are thus considered ordinary, so the RE in @var{pattern} is a
literal string.  This is an extension, compatible with but not specified
by POSIX 1003.2, and should be used with caution in software intended to
be portable to other systems.  @code{REG_EXTENDED} and @code{REG_NOSPEC}
may not be used in the same call to @code{regcomp}.

@item REG_ICASE

Compile for matching that ignores upper/lower case distinctions.  See
the description of regular expressions below for details of
case-independent matching.

@item REG_NOSUB

Compile for matching that need only report success or failure, not what
was matched.

@item REG_NEWLINE

Compile for newline-sensitive matching.  By default, newline is a
completely ordinary character with no special meaning in either REs or
strings.  With this flag, @samp{[^} bracket expressions and @samp{.}
never match newline, a @samp{^} anchor matches the null string after any
newline in the string in addition to its normal function, and the
@samp{$} anchor matches the null string before any newline in the string
in addition to its normal function.

@item REG_PEND

The regular expression ends, not at the first NUL, but just before the
character pointed to by the @code{re_endp} member of the structure
pointed to by @var{preg}.  The @code{re_endp} member is of type
@samp{const char *}.  This flag permits inclusion of NULs in the RE;
they are considered ordinary characters.  This is an extension,
compatible with but not specified by POSIX 1003.2, and should be used
with caution in software intended to be portable to other systems.

@end table

When successful, @code{regcomp} returns 0 and fills in the structure
pointed to by @var{preg}.  One member of that structure (other than
@code{re_endp}) is publicized: @code{re_nsub}, of type @code{size_t},
contains the number of parenthesized subexpressions within the RE
(except that the value of this member is undefined if the
@code{REG_NOSUB} flag was used).

Note that the length of the RE does matter; in particular, there is a
strong speed bonus for keeping RE length under about 30 characters,
with most special characters counting roughly double.

@subheading Return Value

If @code{regcomp} succeeds, it returns zero; if it fails, it returns a
non-zero error code, which is one of these:

@table @code

@item REG_BADPAT

invalid regular expression

@item REG_ECOLLATE

invalid collating element

@item REG_ECTYPE

invalid character class

@item REG_EESCAPE

@samp{\} applied to unescapable character

@item REG_ESUBREG

invalid backreference number (e.g., larger than the number of
parenthesized subexpressions in the RE)

@item REG_EBRACK

brackets [ ] not balanced

@item REG_EPAREN

parentheses ( ) not balanced

@item REG_EBRACE

braces @{ @} not balanced

@item REG_BADBR

invalid repetition count(s) in @{ @}

@item REG_ERANGE

invalid character range in [ ]

@item REG_ESPACE

ran out of memory (an RE like, say,
@samp{((((a@{1,100@})@{1,100@})@{1,100@})@{1,100@})@{1,100@}'} will
eventually run almost any existing machine out of swap space)

@item REG_BADRPT

?, *, or + operand invalid

@item REG_EMPTY

empty (sub)expression

@item REG_ASSERT

``can't happen'' (you found a bug in @code{regcomp})

@item REG_INVARG

invalid argument (e.g. a negative-length string)

@end table

@subheading Regular Expressions' Syntax

Regular expressions (@dfn{RE}s), as defined in POSIX 1003.2, come in two
forms: modern REs (roughly those of @code{egrep}; 1003.2 calls these
@emph{extended} REs) and obsolete REs (roughly those of @code{ed};
1003.2 @emph{basic} REs).  Obsolete REs mostly exist for backward
compatibility in some old programs; they will be discussed at the end.
1003.2 leaves some aspects of RE syntax and semantics open; `(*)' marks
decisions on these aspects that may not be fully portable to other
1003.2 implementations.

A (modern) RE is one(*) or more non-empty(*) @emph{branches}, separated
by @samp{|}.  It matches anything that matches one of the branches.

A branch is one(*) or more @emph{pieces}, concatenated.  It matches a
match for the first, followed by a match for the second, etc.

A piece is an @emph{atom} possibly followed by a single(*) `*', `+',
`?', or @emph{bound}.
An atom followed by `*' matches a sequence of 0 or more matches of the atom.
An atom followed by `+' matches a sequence of 1 or more matches of the atom.
An atom followed by `?' matches a sequence of 0 or 1 matches of the atom.

A @emph{bound} is `@{' followed by an unsigned decimal integer, possibly
followed by `,' possibly followed by another unsigned decimal integer,
always followed by `@}'.  The integers must lie between 0 and
@code{RE_DUP_MAX} (255(*)) inclusive, and if there are two of them, the
first may not exceed the second.  An atom followed by a bound containing
one integer @samp{i} and no comma matches a sequence of exactly @samp{i}
matches of the atom.  An atom followed by a bound containing one integer
@samp{i} and a comma matches a sequence of @samp{i} or more matches of
the atom.  An atom followed by a bound containing two integers @samp{i}
and @samp{j} matches a sequence of @samp{i} through @samp{j} (inclusive)
matches of the atom.

An atom is a regular expression enclosed in `()' (matching a match for the
regular expression), an empty set of `()' (matching the null string(*)),
a @emph{bracket expression} (see below), `.' (matching any single
character), `^' (matching the null string at the beginning of a line),
`$' (matching the null string at the end of a line), a `\\' followed by
one of the characters `^.[$()|*+?@{\\' (matching that character taken as
an ordinary character), a `\\' followed by any other character(*)
(matching that character taken as an ordinary character, as if the `\\'
had not been present(*)), or a single character with no other
significance (matching that character).  A `@{' followed by a character
other than a digit is an ordinary character, not the beginning of a
bound(*).  It is illegal to end an RE with `\\'.

A @emph{bracket expression} is a list of characters enclosed in `[]'.
It normally matches any single character from the list (but see below).
If the list begins with `^', it matches any single character (but see
below) @emph{not} from the rest of the list.  If two characters in the
list are separated by `-', this is shorthand for the full @emph{range}
of characters between those two (inclusive) in the collating sequence,
e.g. `[0-9]' in ASCII matches any decimal digit.  It is illegal(*) for
two ranges to share an endpoint, e.g. `a-c-e'.  Ranges are very
collating-sequence-dependent, and portable programs should avoid relying
on them.

To include a literal `]' in the list, make it the first character
(following a possible `^').  To include a literal `-', make it the
first or last character, or the second endpoint of a range.  To use a
literal `-' as the first endpoint of a range, enclose it in `[.' and
`.]' to make it a collating element (see below).  With the exception of
these and some combinations using `[' (see next paragraphs), all other
special characters, including `\\', lose their special significance
within a bracket expression.

Within a bracket expression, a collating element (a character, a
multi-character sequence that collates as if it were a single character,
or a collating-sequence name for either) enclosed in `[.' and `.]'
stands for the sequence of characters of that collating element.  The
sequence is a single element of the bracket expression's list.  A
bracket expression containing a multi-character collating element can
thus match more than one character, e.g. if the collating sequence
includes a `ch' collating element, then the RE @samp{[[.ch.]]*c} matches
the first five characters of ``chchcc''.

Within a bracket expression, a collating element enclosed in `[=' and
`=]' is an equivalence class, standing for the sequences of characters
of all collating elements equivalent to that one, including itself.
(If there are no other equivalent collating elements, the treatment is
as if the enclosing delimiters were `[.' and `.]'.)  For example, if o
and \o'o^' are the members of an equivalence class, then `[[=o=]]',
`[[=\o'o^'=]]', and `[o\o'o^']' are all synonymous.  An equivalence
class may not\(dg be an endpoint of a range.

Within a bracket expression, the name of a @emph{character class}
enclosed in `[:' and `:]' stands for the list of all characters
belonging to that class.
Standard character class names are:

@example
alnum    digit    punct
alpha    graph    space
blank    lower    upper
cntrl    print    xdigit
@end example

These stand for the character classes defined by @code{isalnum}
(@pxref{isalnum}), @code{isdigit} (@pxref{isdigit}), @code{ispunct}
(@pxref{ispunct}), @code{isalpha} (@pxref{isalpha}), @code{isgraph}
(@pxref{isgraph}), @code{isspace} (@pxref{isspace}) (@code{blank} is the
same as @code{space}), @code{islower} (@pxref{islower}), @code{isupper}
(@pxref{isupper}), @code{iscntrl} (@pxref{iscntrl}), @code{isprint}
(@pxref{isprint}), and @code{isxdigit} (@pxref{isxdigit}),
respectively.  A locale may provide others.  A character class may not
be used as an endpoint of a range.

There are two special cases(*) of bracket expressions: the bracket
expressions `[[:<:]]' and `[[:>:]]' match the null string at the
beginning and end of a word respectively.  A word is defined as a
sequence of word characters which is neither preceded nor followed by
word characters.  A word character is an @code{alnum} character (as
defined by @code{isalnum} library function) or an underscore.  This is
an extension, compatible with but not specified by POSIX 1003.2, and
should be used with caution in software intended to be portable to other
systems.

In the event that an RE could match more than one substring of a given
string, the RE matches the one starting earliest in the string.  If the
RE could match more than one substring starting at that point, it
matches the longest.  Subexpressions also match the longest possible
substrings, subject to the constraint that the whole match be as long as
possible, with subexpressions starting earlier in the RE taking priority
over ones starting later.  Note that higher-level subexpressions thus
take priority over their lower-level component subexpressions.

Match lengths are measured in characters, not collating elements.  A
null string is considered longer than no match at all.  For example,
@samp{bb*} matches the three middle characters of @samp{abbbc},
@samp{(wee|week)(knights|nights)} matches all ten characters of
@samp{weeknights}, when @samp{(.*).*} is matched against @samp{abc} the
parenthesized subexpression matches all three characters, and when
@samp{(a*)*} is matched against `bc' both the whole RE and the
parenthesized subexpression match the null string.

If case-independent matching is specified, the effect is much as if all
case distinctions had vanished from the alphabet.  When an alphabetic
that exists in multiple cases appears as an ordinary character outside a
bracket expression, it is effectively transformed into a bracket
expression containing both cases, e.g. `x' becomes `[xX]'.  When it
appears inside a bracket expression, all case counterparts of it are
added to the bracket expression, so that (e.g.) `[x]' becomes `[xX]' and
`[^x]' becomes `[^xX]'.

No particular limit is imposed on the length of REs(*).  Programs
intended to be portable should not employ REs longer than 256 bytes,
as an implementation can refuse to accept such REs and remain
POSIX-compliant.

Obsolete (@emph{basic}) regular expressions differ in several respects.
`|', `+', and `?' are ordinary characters and there is no equivalent
for their functionality.  The delimiters for bounds are `\\@{' and
`\\@}', with `@{' and `@}' by themselves ordinary characters.  The
parentheses for nested subexpressions are `\(' and `\)', with `(' and
`)' by themselves ordinary characters.  `^' is an ordinary character
except at the beginning of the RE or(*) the beginning of a parenthesized
subexpression, `$' is an ordinary character except at the end of the RE
or(*) the end of a parenthesized subexpression, and `*' is an ordinary
character if it appears at the beginning of the RE or the beginning of a
parenthesized subexpression (after a possible leading `^').
Finally, there is one new type of atom, a @emph{back reference}:
`\\' followed by a non-zero decimal digit @emph{d} matches the same
sequence of characters matched by the @emph{d}th parenthesized
subexpression (numbering subexpressions by the positions of their
opening parentheses, left to right), so that (e.g.) @samp{\\([bc]\\)\\1}
matches `bb' or `cc' but not `bc'.

@c -------------------------------------------------------------------------

@node regexec, string
@subheading Syntax

@example
#include <sys/types.h>
#include <regex.h>

int regexec(const regex_t *preg, const char *string,
            size_t nmatch, regmatch_t pmatch[], int eflags);
@end example


@subheading Description

@code{regexec} matches the compiled RE pointed to by @var{preg} against
the @var{string}, subject to the flags in @var{eflags}, and reports
results using @var{nmatch}, @var{pmatch}, and the returned value.  The
RE must have been compiled by a previous invocation of @code{regcomp}
(@pxref{regcomp}).  The compiled form is not altered during execution of
@code{regexec}, so a single compiled RE can be used simultaneously by
multiple threads.

By default, the NUL-terminated string pointed to by @var{string} is
considered to be the text of an entire line, minus any terminating
newline.

The @var{eflags} argument is the bitwise OR of zero or more of the
following flags:

@table @code

@item REG_NOTBOL

The first character of the string is not the beginning of a line, so the
`^' anchor should not match before it.  This does not affect the
behavior of newlines under @code{REG_NEWLINE} (REG_NEWLINE,
@pxref{regcomp}).

@item REG_NOTEOL

The NUL terminating the string does not end a line, so the `$' anchor
should not match before it.  This does not affect the behavior of
newlines under @code{REG_NEWLINE} (REG_NEWLINE, @pxref{regcomp}).

@item REG_STARTEND

The string is considered to start at @var{@w{string + pmatch[0].rm_so}}
and to have a terminating @code{NUL} located at
@var{@w{string + pmatch[0].rm_eo}} (there need not actually be a
@code{NUL} at that location), regardless of the value of @var{nmatch}.
See below for the definition of @var{pmatch} and @var{nmatch}.  This is
an extension, compatible with but not specified by POSIX 1003.2, and
should be used with caution in software intended to be portable to other
systems.  Note that a non-zero @code{rm_so} does not imply
@code{REG_NOTBOL}; @code{REG_STARTEND} affects only the location of the
string, not how it is matched.

@item REG_TRACE

trace execution (printed to stdout)

@item REG_LARGE

force large representation

@item REG_BACKR

force use of backref code

@end table

Regular Expressions' Syntax, @xref{regcomp}, for a discussion of what is
matched in situations where an RE or a portion thereof could match any
of several substrings of @var{string}.

If @code{REG_NOSUB} was specified in the compilation of the RE
(REG_NOSUB, @pxref{regcomp}), or if @var{nmatch} is 0, @code{regexec}
ignores the @var{pmatch} argument (but see below for the case where
@code{REG_STARTEND} is specified).  Otherwise, @var{pmatch} should point
to an array of @var{nmatch} structures of type @code{regmatch_t}.  Such
a structure has at least the members @code{rm_so} and @code{rm_eo}, both
of type @code{regoff_t} (a signed arithmetic type at least as large as
an @code{off_t} and a @code{ssize_t}, containing respectively the offset
of the first character of a substring and the offset of the first
character after the end of the substring.  Offsets are measured from the
beginning of the @var{string} argument given to @code{regexec}.  An
empty substring is denoted by equal offsets, both indicating the
character following the empty substring.

When @code{regexec} returns, the 0th member of the @var{pmatch} array is
filled in to indicate what substring of @var{string} was matched by the
entire RE.  Remaining members report what substring was matched by
parenthesized subexpressions within the RE; member @code{i} reports
subexpression @code{i}, with subexpressions counted (starting at 1) by
the order of their opening parentheses in the RE, left to right.  Unused
entries in the array---corresponding either to subexpressions that did
not participate in the match at all, or to subexpressions that do not
exist in the RE (that is, @code{@w{i > preg->re_nsub}}---have both
@code{rm_so} and @code{rm_eo} set to @code{-1}.  If a subexpression
participated in the match several times, the reported substring is the
last one it matched.  (Note, as an example in particular, that when the
RE @samp{(b*)+} matches @samp{bbb}, the parenthesized subexpression
matches each of the three `b's and then an infinite number of empty
strings following the last `b', so the reported substring is one of the
empties.)

If @code{REG_STARTEND} is specified in @var{eflags}, @var{pmatch} must
point to at least one @code{regmatch_t} variable (even if @var{nmatch}
is 0 or @code{REG_NOSUB} was specified in the compilation of the RE,
REG_NOSUB, @pxref{regcomp}), to hold the input offsets for
@code{REG_STARTEND}.  Use for output is still entirely controlled by
@var{nmatch}; if @var{nmatch} is 0 or @code{REG_NOSUB} was specified,
the value of @code{pmatch[0]} will not be changed by a successful
@code{regexec}.

@var{nmatch} exceeding 0 is expensive; @var{nmatch} exceeding 1 is
worse.  Back references are massively expensive.

@subheading Return Value

Normally, @code{regexec} returns 0 for success and the non-zero code
@code{REG_NOMATCH} for failure.  Other non-zero error codes may be
returned in exceptional situations.  The list of possible error return
values is below:

@table @code

@item REG_ESPACE

ran out of memory

@item REG_BADPAT

the passed argument @var{preg} doesn't point to an RE compiled by
@code{regcomp}

@item REG_INVARG

invalid argument(s) (e.g., @var{@w{string + pmatch[0].rm_eo}} is less
than @var{@w{string + pmatch[0].rm_so}})

@end table

@c ----------------------------------------------------------------------

@node regerror, string
@subheading Syntax

@example

#include <sys/types.h>
#include <regex.h>

size_t regerror(int errcode, const regex_t *preg,
                char *errbuf, size_t errbuf_size);

@end example

@subheading Description

@code{regerror} maps a non-zero value of @var{errcode} from either
@code{regcomp} (Return Value, @pxref{regcomp}) or @code{regexec}
(Return Value, @pxref{regexec}) to a human-readable, printable message.

If @var{preg} is non-@code{NULL}, the error code should have arisen from
use of the variable of the type @code{regex_t} pointed to by @var{preg},
and if the error code came from @code{regcomp}, it should have been the
result from the most recent @code{regcomp} using that @code{regex_t}
variable.  (@code{regerror} may be able to supply a more detailed
message using information from the @code{regex_t} than from
@var{errcode} alone.)  @code{regerror} places the @code{NUL}-terminated
message into the buffer pointed to by @var{errbuf}, limiting the length
(including the @code{NUL}) to at most @var{errbuf_size} bytes.  If the
whole message won't fit, as much of it as will fit before the
terminating @code{NUL} is supplied.  In any case, the returned value is
the size of buffer needed to hold the whole message (including
terminating @code{NUL}).  If @var{errbuf_size} is 0, @var{errbuf} is
ignored but the return value is still correct.

If the @var{errcode} given to @code{regerror} is first ORed with
@code{REG_ITOA}, the ``message'' that results is the printable name of
the error code, e.g. ``REG_NOMATCH'', rather than an explanation
thereof.  If @var{errcode} is @code{REG_ATOI}, then @var{preg} shall be
non-NULL and the @code{re_endp} member of the structure it points to
must point to the printable name of an error code
(e.g. ``REG_ECOLLATE''); in this case, the result in @var{errbuf} is the
decimal representation of the numeric value of the error code (0 if the
name is not recognized).  @code{REG_ITOA} and @code{REG_ATOI} are
intended primarily as debugging facilities; they are extensions,
compatible with but not specified by POSIX 1003.2, and should be used
with caution in software intended to be portable to other systems.  Be
warned also that they are considered experimental and changes are
possible.

@subheading Return Value

The size of buffer needed to hold the message (including terminating
@code{NUL}) is always returned, even if @var{errbuf_size} is zero.

@c --------------------------------------------------------------------------

@node regfree, string
@subheading Syntax

@example

#include <sys/types.h>
#include <regex.h>

void regfree(regex_t *preg);

@end example

@subheading Description

@code{regfree} frees any dynamically-allocated storage associated with
the compiled RE pointed to by @var{preg}.  The remaining @code{regex_t}
is no longer a valid compiled RE and the effect of supplying it to
@code{regexec} or @code{regerror} is undefined.