# Tcl_RegExpMatch, Tcl_RegExpCompile, Tcl_RegExpExec, Tcl_RegExpRange - Pattern matching with regular expressions

## SYNOPSIS

    #include <tcl.h>

    int
    Tcl_RegExpMatch(interp, string, pattern)

    Tcl_RegExp
    Tcl_RegExpCompile(interp, pattern)

    int
    Tcl_RegExpExec(interp, regexp, string, start)

    Tcl_RegExpRange(regexp, index, startPtr, endPtr)

## ARGUMENTS

Tcl_Interp *interp (in)
  Tcl interpreter to use for error reporting.

char *string (in)
  String to check for a match with a regular expression.

char *pattern (in)
  String in the form of a regular expression pattern.

Tcl_RegExp regexp (in)
  Compiled regular expression. Must have been returned previously by Tcl_RegExpCompile.

char *start (in)
  If string is just a portion of some other string, this argument identifies the beginning of the larger string. If it isn't the same as string, then no ^ matches will be allowed.

int index (in)
  Specifies which range is desired: 0 means the range of the entire match, 1 or greater means the range that matched a parenthesized sub-expression.

char **startPtr (out)
  The address of the first character in the range is stored here, or NULL if there is no such range.

char **endPtr (out)
  The address of the character just after the last one in the range is stored here, or NULL if there is no such range.

## DESCRIPTION

Tcl_RegExpMatch determines whether its pattern argument matches regexp, where regexp is interpreted as a regular expression using the same rules as for the regexp Tcl command. If there is a match then Tcl_RegExpMatch returns 1. If there is no match then Tcl_RegExpMatch returns 0. If an error occurs in the matching process (e.g. pattern is not a valid regular expression) then Tcl_RegExpMatch returns -1 and leaves an error message in interp->result.

Tcl_RegExpCompile, Tcl_RegExpExec, and Tcl_RegExpRange provide lower-level access to the regular expression pattern matcher. Tcl_RegExpCompile compiles a regular expression string into the internal form used for efficient pattern matching. The return value is a token for this compiled form, which can be used in subsequent calls to Tcl_RegExpExec or Tcl_RegExpRange. If an error occurs while compiling the regular expression then Tcl_RegExpCompile returns NULL and leaves an error message in interp->result.

Tcl_RegExpExec executes the regular expression pattern matcher. It returns 1 if string contains a range of characters that match regexp, 0 if no match is found, and -1 if an error occurs. In the case of an error, Tcl_RegExpExec leaves an error message in interp->result. When searching a string for multiple matches of a pattern, it is important to distinguish between the start of the original string and the start of the current search. For example, when searching for the second occurrence of a match, the string argument might point to the character just after the first match; however, it is important for the pattern matcher to know that this is not the start of the entire string, so that it doesn't allow ^ atoms in the pattern to match. The start argument provides this information by pointing to the start of the overall string containing string. Start will be less than or equal to string; if it is less than string then no ^ matches will be allowed.

Tcl_RegExpRange may be invoked after Tcl_RegExpExec returns; it provides detailed information about what ranges of the string matched what parts of the pattern. Tcl_RegExpRange returns a pair of pointers in *startPtr and *endPtr that identify a range of characters in the source string for the most recent call to Tcl_RegExpExec. Index indicates which of several ranges is desired: if index is 0, information is returned about the overall range of characters that matched the entire pattern; otherwise, information is returned about the range of characters that matched the index'th parenthesized subexpression within the pattern. If there is no range corresponding to index then NULL is stored in *firstPtr and *lastPtr.

## KEYWORDS

match, pattern, regular expression, string, subexpression