| Member Functions |
| index() operator=() status() |
#include <rw/regexp.h>
RWCRegexp re(".*\\.doc");// Matches filename with suffix ".doc"
Class RWCRegexp represents a regular expression. The constructor "compiles" the expression into a form that can be used more efficiently. The results can then be used for string searches using class RWCString.
The regular expression (RE) is constucted as follows:
The following rules determine one-character REs that match a single character:
| 1.1 | Any character that is not a special character (to be defined) matches itself. |
| 1.2 | A backslash (\) followed by any special character matches the literal character itself. I.e., this "escapes" the special character. |
| 1.3 | The "special characters" are:
+ * ? . [ ] ^ $ |
| 1.4 | The period (.) matches any character except the newline. E.g., ".umpty" matches either "Humpty" or "Dumpty." |
| 1.5 | A set of characters enclosed in brackets ([]) is a one-character RE that matches any of the characters in that set. E.g., "[akm]" matches either an "a", "k", or "m". A range of characters can be indicated with a dash. E.g., "[a-z]" matches any lower-case letter. However, if the first character of the set is the caret (^), then the RE matches any character except those in the set. It does not match the empty string. Example: [^akm] matches any character except "a", "k", or "m". The caret loses its special meaning if it is not the first character of the set. |
The following rules can be used to build a multicharacter RE.
| 2.1 | A one-character RE followed by an asterisk (*) matches zero or more occurrences of the RE. Hence, [a-z]* matches zero or more lower-case characters. |
| 2.2 | A one-character RE followed by a plus (+) matches one or more occurrences of the RE. Hence, [a-z]+ matches one or more lower-case characters. |
| 2.3 | A question mark (?) is an optional element. The preceeding RE can occur zero or once in the string -- no more. E.g. xy?z matches either xyz or xz. |
| 2.4 | The concatenation of REs is a RE that matches the corresponding concatenation of strings. E.g., [A-Z][a-z]* matches any capitalized word. |
Finally, the entire regular expression can be anchored to match only the beginning or end of a line:
| 3.1 | If the caret (^) is at the beginning of the RE, then the matched string must be at the beginning of a line. |
| 3.2 | If the dollar sign ($) is at the end of the RE, then the matched string must be at the end of the line. |
The following escape codes can be used to match control characters:
| \b | backspace |
| \e | ESC (escape) |
| \f | formfeed |
| \n | newline |
| \r | carriage return |
| \t | tab |
| \xddd | the literal hex number 0xdd |
| \ddd | the literal octal number ddd |
| \^C | Control code. E.g. \^D is "control-D" |
The most frequent problem with use of this class is in being able to specify a backslash character to be parsed. If you are attempting to parse a regular expression that contains backslashes, you must be aware that the C++ compiler and the regular expression constructor will both assume that any backslashes they see are intended to escape the following character. Thus, to specify a regular expression that exactly matches "a\a", you would have to create the regular expression using four backslashes as follows: the regular expression needs to see "a\\a", and for that to happen, the compiler would have to see "a\\\\a".
RWCRegexp reg("a\\\\a");
^|^|
1 2
The backslashes marked with a ^ are an escape for the compiler, and the ones marked with | will thus be seen by the regular expression parser. At that point, the backslash marked 1 is an escape, and the one marked 2 will actually be put into the regular expression.
Similarly, if you really need to escape a character, such as a ".", you will have to pass two backslashes to the compiler:
RWCRegexp regDot("\\.")
^|
Once again, the backslash marked ^ is an escape for the compiler, and the one marked with | will be seen by the regular expression constructor as an escape for the following ".".
None
#include <rw/regexp.h>
#include <rw/cstring.h>
#include <rw/rstream.h>
main(){
RWCString aString("Hark! Hark! the lark");
// A regular expression matching any lower-case word
// starting with "l":
RWCRegexp reg("l[a-z]*");
cout << aString(reg) << endl; // Prints "lark"
}
RWCRegexp(const char* pat);
Construct a regular expression from the pattern given by pat. The status of the results can be found by using member function status().
RWCRegexp(const RWCRegexp& r);
Copy constructor. Uses value semantics -- self will be a copy of r.
~RWCRegexp();
Destructor. Releases any allocated memory.
RWCRegexp& operator=(const RWCRegexp&);
Uses value semantics -- sets self to a copy of r.
RWCRegexp& operator=(const char* pat);
Recompiles self to the pattern given by pat. The status of the results can be found by using member function status().
size_t index(const RWCString& str,size_t* len, size_t start=0) const;
Returns the index of the first instance in the string str that matches the regular expression compiled in self, or RW_NPOS if there is no such match. The search starts at index start. The length of the matching pattern is returned in the variable pointed to by len. If an invalid regular expression is used for the search, an exception of type RWInternalErr will be thrown. Note that this member function is relatively clumsy to use -- class RWCString offers a better interface to regular expression searches.
statVal status();
Returns the status of the regular expression and resets status to OK:
|
statVal |
Meaning |
|
RWCRegexp::OK |
No errors |
|
RWCRegexp::ILLEGAL |
Pattern was illegal |
|
RWCRegexp::TOOLONG |
Pattern exceeded maximum length
[3] |