https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111129
Bug ID: 111129
Summary: std::regex incorrectly matches quantifiers with plus
appended
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: gcc at octaforge dot org
Target Milestone: ---
Example code:
```
#include <cstdio>
#include <string>
#include <regex>
int main(void) {
std::smatch matches;
auto re = std::regex(R"(a++)", std::regex::icase);
std::string inp = "aaa";
std::regex_search(inp, matches, re);
for (auto &match: matches) {
printf("%s\n", match.str().data());
}
}
```
With libstdc++, this does not crash, and outputs 'aaa'.
This gives people a false idea that libstdc++ implements possessive quantifiers
(see e.g. https://github.com/wwmm/easyeffects/pull/2536) despite the
documentation or code having no references to any such extension (and the C++
standard likewise not mentioning it). You can verify that the semantics are not
possessive by changing the pattern to 'a++a', which should with possessive
semantics not match anything, but with libstdc++ it's an identical match as
before.
With libc++, this correctly fails with: libc++abi: terminating due to uncaught
exception of type std::__1::regex_error: One of *?+{ was not preceded by a
valid regular expression.
