Content-type: text/html Man page of regcmp


Section: Standard C Library Functions (3C)
Updated: 14 Nov 2002
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regcmp, regex - compile and execute regular expression  


#include <libgen.h>

char *regcmp(const char *string1, /* char *string2 */ ..., int /*(char*)0*/);

char *regex(const char *re, const char *subject, /* char *ret0 */ ...);

extern char *__loc1;



The regcmp() function compiles a regular expression (consisting of the concatenated arguments) and returns a pointer to the compiled form. The malloc(3C) function is used to create space for the compiled form. It is the user's responsibility to free unneeded space so allocated. A NULL return from regcmp() indicates an incorrect argument. regcmp(1) has been written to generally preclude the need for this routine at execution time.

The regex() function executes a compiled pattern against the subject string. Additional arguments are passed to receive values back. The regex() function returns NULL on failure or a pointer to the next unmatched character on success. A global character pointer __loc1 points to where the match began. The regcmp() and regex() functions were mostly borrowed from the editor ed(1); however, the syntax and semantics have been changed slightly. The following are the valid symbols and associated meanings.

[]*.^ This group of symbols retains its meaning as described on the regexp(5) manual page.

$ Matches the end of the string; \n matches a newline.

- Within brackets the minus means through. For example, [a-z] is equivalent to []. The - can appear as itself only if used as the first or last character. For example, the character class expression []-] matches the characters ] and -.

+ A regular expression followed by + means one or more times. For example, [0-9]+ is equivalent to [0-9][0-9]*.

{m} {m,} {m,u} Integer values enclosed in {} indicate the number of times the preceding regular expression is to be applied. The value m is the minimum number and u is a number, less than 256, which is the maximum. If only m is present (that is, {m}), it indicates the exact number of times the regular expression is to be applied. The value {m,} is analogous to {m,infinity}. The plus ( +) and star (*) operations are equivalent to {1,} and {0,} respectively.

( ... )$n The value of the enclosed regular expression is to be returned. The value will be stored in the (n+1)th argument following the subject argument. At most, ten enclosed regular expressions are allowed. The regex() function makes its assignments unconditionally.

( ... ) Parentheses are used for grouping. An operator, for example, *, +, {}, can work on a single character or a regular expression enclosed in parentheses. For example, (a*(cb+)*)$0. By necessity, all the above defined symbols are special. They must, therefore, be escaped with a \ (backslash) to be used as themselves.



Example 1: Example matching a leading newline in the subject string.

The following example matches a leading newline in the subject string pointed at by cursor.


char *cursor, *newcursor, *ptr;
newcursor = regex((ptr = regcmp("^\n", (char *)0)), cursor);


The following example matches through the string Testing3 and returns the address of the character after the last matched character (the ``4''). The string Testing3 is copied to the character array ret0.


char ret0[9];
char *newcursor, *name;
name = regcmp("([A-Za-z][A-za-z0-9]{0,7})$0", (char *)0);
newcursor = regex(name, "012Testing345", ret0);


The following example applies a precompiled regular expression in file.i (see regcmp(1)) against string.


#include "file.i"
char *string, *newcursor;
newcursor = regex(name, string);



See attributes(5) for descriptions of the following attributes:




ed(1), regcmp(1), malloc(3C), attributes(5), regexp(5)  


The user program may run out of memory if regcmp() is called iteratively without freeing the vectors no longer required.

When compiling multithreaded applications, the _REENTRANT flag must be defined on the compile line. This flag should only be used in multithreaded applications.




This document was created by man2html, using the manual pages.
Time: 02:37:22 GMT, October 02, 2010