boost::xpressive::before — Look-ahead assertion.
template<typename Xpr> unspecified before(Xpr const & xpr);
before(xpr) succeeds if the xpr sub-expression would match at the current position in the sequence, but xpr is not included in the match. For instance, before("foo") succeeds if we are before a "foo". Look-ahead assertions can be negated with the bit-compliment operator.
before(xpr) is equivalent to the perl (?=...) extension. ~before(xpr) is a negative look-ahead assertion, equivalent to the perl (?!...) extension.
|Copyright © 2003, 2004 Eric Niebler|