FBB::Pattern(3bobcat)
Pattern matcher
(libbobcat-dev_6.04.00)
2005-2023
NAME
FBB::Pattern - Performs RE pattern matching
SYNOPSIS
#include <bobcat/pattern>
Linking option: -lbobcat
DESCRIPTION
Pattern objects may be used for Regular Expression (RE) pattern
matching. The class is a wrapper around the regcomp(3) family of
functions. By default it uses `extended regular expressions', requiring you to
escape multipliers and bounding-characters when they should be interpreted as
ordinary characters (i.e., *, +, ?, ^, $, |, (, ), [, ], {, } should be
escaped when used as literal characters).
The Pattern class supports the use of the following (Perl-like)
special escape sequences:
\b - indicating a word-boundary
\d - indicating a digit ([[:digit:]]) character
\s - indicating a white-space ([:space:]) character
\w - indicating a word ([:alnum:]) character
The corresponding capitals (e.g., \W) define the complementary
character sets. The capitalized character set shorthands are not expanded
inside explicit character-classes (i.e., [ ... ] constructions). So
[\W] represents a set of two characters: \ and W.
As the backslash (\) is treated as a special character it should be
handled carefully. Pattern converts the escape sequences \d \s \w (and
outside of explicit character classes the sequences \D \S \W) to their
respective character classes. All other escape sequences are kept as-is, and
the resulting regular expression is offered to the pattern matching
compilation function regcomp(3). This function interprets
escape sequences. Consequently some care should be exercised when defining
patterns containing escape sequences. Here are the rules:
- Special escape sequences (like \d) are converted to character
classes. E.g.,
---------------------------------------------------------
Specify: Converts to: regcomp uses: Matches:
---------------------------------------------------------
\d [[:digit:]] [[:digit:]] 3
---------------------------------------------------------
- Ordinary escape sequences (like \x) are kept as-is. E.g.,
---------------------------------------------------------
Specify: Converts to: regcomp uses: Matches:
---------------------------------------------------------
\x \x x x
---------------------------------------------------------
- To specify literal escape sequences, Raw String Literals are advised,
as they don't require doubling escape sequences. E.g., the following
regular expression matches an (alpha-numeric) word, followed by optional
blanks, a colon, more optional blanks and a (decimal) number:
R"((\w+)\s*:\s*\d+)"
NAMESPACE
FBB
All constructors, members, operators and manipulators, mentioned in this
man-page, are defined in the namespace FBB.
INHERITS FROM
-
TYPEDEF
- Pattern::Position:
A nested type representing the offsets of the first character and
the offset beyond the last character of the matched text or indexed
subexpression, defined as std::pair<std::string::size_type,
std::string::size_type>.
CONSTRUCTORS
- Pattern():
The default constructor defines no pattern, but is available as a
placeholder for, e.g., containers requiring default constructors. A
Pattern object thus constructed cannot be used to match patterns, but can
be the lvalue in assignments where another Pattern object is the
rvalue. However, it can receive a pattern using the member
setPattern() (see below). An FBB::Exception object is thrown if the
object could not be constructed.
- Pattern(std::string const &pattern,
bool caseSensitive = true,
size_t nSub = 10,
int options = REG_EXTENDED | REG_NEWLINE):
This constructor compiles pattern, preparing the Pattern
object for pattern matches. The second parameter determines whether case
sensitive matching will be used (the default) or not. Subexpressions are
defined by parentheses pairs. Each matching pair defines a subexpression,
where the order-number of their opening parentheses determines the
subexpression's index. By default at most 10 subexpressions are recognized.
The options flags may be:
REG_EXTENDED:
Use POSIX Extended Regular Expression syntax when
interpreting regex. If not set, POSIX Basic Regular
Expression syntax is used.
REG_NOSUB:
Support for substring addressing of matches is not
required. The nmatch and pmatch parameters to
regexec are ignored if the pattern buffer supplied
was compiled with this flag set.
REG_NEWLINE:
Match-any-character operators don't match a newline.
A non-matching list ([^...]) not containing a newline
does not match a newline.
Match-beginning-of-line operator (^) matches the empty
string immediately after a newline, regardless of whether
eflags, the execution flags of regexec, contains
REG_NOTBOL.
Match-end-of-line operator ($) matches the empty
string immediately before a newline, regardless of
whether eflags contains REG_NOTEOL.
Copy and move constructors (and assignment operators) are available.
MEMBER FUNCTIONS
All members of std::ostringstream and std::exception are
available, as Pattern inherits from these classes.
- std::string before() const:
Following a successful match, before() returns the text before the
matched text.
- std::string beyond() const:
Following a successful match, beyond() returns the text beyond the
matched text.
- size_t end() const:
Returns the number of matched elements (text and
subexpressions). end() is the lowest index value for which position()
returns two std::string::npos values (see the position() member
function, below).
- void match(std::string const &text, int options = 0):
Match a string with a pattern. If the text could not be matched, an
Exception exception is thrown , using Pattern::match() as its
prefix-text.
Options may be:
REG_NOTBOL:
The match-beginning-of-line operator always fails to match
(but see the compilation flag REG_NEWLINE above) This flag
may be used when different portions of a string are passed
to regexec and the beginning of the string should not be
interpreted as the beginning of the line.
REG_NOTEOL:
The match-end-of-line operator always fails to
match (but see the compilation flag REG_NEWLINE)
- std::string matched() const:
Following a successful match, this function returns the matched text.
- std::string const &pattern() const:
This member function returns the pattern that is offered to
regcomp(3). It returns the content of a static string that is
overwritten at each construction of a Pattern object and at each call of
the setPattern() member function.
- Pattern::Position position(size_t index) const:
With index == 0 the fully matched text is returned (identical to
matched()). Other index values return the corresponding
subexpressions. std::string::npos, std::string::npos is returned if index
is at least end() (which may happen at index value 0).
- void setPattern(std::string const &pattern,
bool caseSensitive = true,
size_t nSub = 10,
int options = REG_EXTENDED | REG_NEWLINE):
This member function installs a new compiled pattern in its
Pattern object. This member's parameters are identical to the second
constructor's parameters. Refer to that constructor for details about the
parameters. Like the constructor, an FBB::Exception exception is thrown if
the new pattern could not be compiled.
- void swap(Pattern &other):
The content of the current object and the other object are
swapped.
OVERLOADED OPERATORS
- std::string operator[](size_t index) const:
Returns the matched text (for index 0) or the text of a
subexpression. An empty string is returned for index values which are at least
end().
- Pattern &operator<<(int matchOptions):
Defines match-options to be used with the following overloaded
operator.
- bool operator<<(std::string const &text):
Performs a match(text, matchOptions) call, catching any exception
that might be thrown. If no matchOptions were set using the above
overloaded operator, none are used. The options set this way are not `sticky':
when necessary, they have to be re-inserted before each new pattern
matching. The function returns true if the matching was successful,
false otherwise.
EXAMPLE
#include "driver.h"
#include <bobcat/pattern>
using namespace std;
using namespace FBB;
#include <algorithm>
#include <cstring>
void showSubstr(string const &str)
{
static int count = 0;
cout << "String " << ++count << " is '" << str << "'\n";
}
void match(Pattern const &patt, string const &text)
try
{
Pattern pattern{ patt };
pattern.match(text);
Pattern p3(pattern);
cout << "before: " << p3.before() << "\n"
"matched: " << p3.matched() << "\n"
"beyond: " << pattern.beyond() << "\n"
"end() = " << pattern.end() << '\n';
for (size_t idx = 0; idx != pattern.end(); ++idx)
{
string str = pattern[idx];
if (str.empty())
cout << "part " << idx << " not present\n";
else
{
Pattern::Position pos = pattern.position(idx);
cout << "part " << idx << ": '" << str << "' (" <<
pos.first << "-" << pos.second << ")\n";
}
}
}
catch (exception const &exc)
{
cout << exc.what() << '\n';
}
int main(int argc, char **argv)
{
string patStr = R"(\d+)";
do
{
cout << "Pattern: '" << patStr << "'\n";
try
{
// by default: case sensitive
// use any args. for case insensitive
Pattern patt(patStr, argc == 1);
cout << "Compiled pattern: " << patt.pattern() << '\n';
while (true)
{
cout << "string to match : ";
string text;
getline(cin, text);
if (text.empty())
break;
cout << "String: '" << text << "'\n";
match(patt, text);
}
}
catch (exception const &exc)
{
cout << exc.what() << ": compilation failed\n";
}
cout << "New pattern: ";
}
while (getline(cin, patStr) and not patStr.empty());
}
FILES
bobcat/pattern - defines the class interface
SEE ALSO
bobcat(7), regcomp(3), regex(3), regex(7)
BUGS
Using Pattern objects as static data members of classes (or as global
objects) is potentially dangerous. If the object files defining these static
data members are stored in a dynamic library they may not be initialized
properly or timely, and their eventual destruction may result in a
segmentation fault. This is a well-known problem with static data, see, e.g.,
http://www.parashift.com/c++-faq-lite/ctors.html#faq-10.15. In situations
like this prefer the use of a (shared, unique) pointer to a Pattern,
initializing the pointer when, e.g., first used.
BOBCAT PROJECT FILES
- https://fbb-git.gitlab.io/bobcat/: gitlab project page;
- bobcat_6.04.00-x.dsc: detached signature;
- bobcat_6.04.00-x.tar.gz: source archive;
- bobcat_6.04.00-x_i386.changes: change log;
- libbobcat1_6.04.00-x_*.deb: debian package containing the
libraries;
- libbobcat1-dev_6.04.00-x_*.deb: debian package containing the
libraries, headers and manual pages;
BOBCAT
Bobcat is an acronym of `Brokken's Own Base Classes And Templates'.
COPYRIGHT
This is free software, distributed under the terms of the
GNU General Public License (GPL).
AUTHOR
Frank B. Brokken (f.b.brokken@rug.nl).