--- /dev/null
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// <regex>
+
+// match_prev_avail:
+// --first is a valid iterator position. When this flag is set the flags
+// match_not_bol and match_not_bow shall be ignored by the regular
+// expression algorithms (30.11) and iterators (30.12)
+
+#include <cassert>
+#include <regex>
+using namespace std;
+
+int main() {
+ char str1[] = "\na";
+ auto str1_scnd = str1 + 1;
+ // Assert that match_prev_avail disables match_not_bol and this matches
+ assert(regex_match(str1 + 1, str1 + 2, regex("^a"),
+ regex_constants::match_not_bol |
+ regex_constants::match_prev_avail));
+ // Manually passing match_prev_avail defines that --str1 is a valid position
+ assert(regex_match(str1_scnd, regex("a"),
+ regex_constants::match_not_bol |
+ regex_constants::match_prev_avail));
+
+ //Assert that match_prev_avail disables match_not_bow and this matches
+ assert(regex_search(str1, regex("\\ba")));
+ assert(regex_match(str1 + 1, str1 + 2, regex("\\ba\\b"),
+ regex_constants::match_not_bow |
+ regex_constants::match_prev_avail));
+ assert(regex_search(str1, regex("\\ba"),
+ regex_constants::match_not_bow |
+ regex_constants::match_prev_avail));
+
+ //Assert that match_prev_avail disables both match_not_bow and match_not_bol
+ assert(regex_match(str1 + 1, str1 + 2, regex("^a"),
+ regex_constants::match_not_bol |
+ regex_constants::match_not_bow |
+ regex_constants::match_prev_avail));
+ assert(regex_match(str1_scnd, regex("\\ba"),
+ regex_constants::match_not_bol |
+ regex_constants::match_not_bow |
+ regex_constants::match_prev_avail));
+
+ // pr 42199
+ string S = " cd";
+ string::iterator Start = S.begin() + 1;
+ string::iterator End = S.end();
+ assert(regex_search(Start, End, regex("^cd")));
+
+ assert(
+ !regex_search(Start, End, regex("^cd"), regex_constants::match_not_bol));
+ assert(!regex_search(Start, End, regex(".*\\bcd\\b"),
+ regex_constants::match_not_bow));
+ assert(!regex_search(Start, End, regex("^cd"),
+ regex_constants::match_not_bol |
+ regex_constants::match_not_bow));
+ assert(!regex_search(Start, End, regex(".*\\bcd\\b"),
+ regex_constants::match_not_bol |
+ regex_constants::match_not_bow));
+
+ assert(regex_search(Start, End, regex("^cd"),
+ regex_constants::match_prev_avail));
+
+ assert(regex_search(Start, End, regex("^cd"),
+ regex_constants::match_not_bol |
+ regex_constants::match_prev_avail));
+ assert(regex_search(Start, End, regex("^cd"),
+ regex_constants::match_not_bow |
+ regex_constants::match_prev_avail));
+ assert(regex_match(Start, End, regex("\\bcd\\b"),
+ regex_constants::match_not_bol |
+ regex_constants::match_not_bow |
+ regex_constants::match_prev_avail));
+ return 0;
+}