std::regex_error at memory location

Question

I have a regex as:

std::regex regexp(
        R"(\$\ part,\ model.*[\n\r]([-]?[0-9]*\.?[0-9]+[Ee]?[-+]?[0-9]*),([-]?[0-9]*\.?[0-9]+[Ee]?[-+]?[0-9]*))",std::regex::extended);

The code compiles, but I receive the following error:

Unhandled exception at 0x748F49C2 in regex.exe: Microsoft C++ exception: std::regex_error at memory location 0x00EFEE30.

I suggest you remove std::regex::extended, use the default ECMAScript flavor. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Jan 25, 2021 at 12:53
Regex flavor has nothing to do with the multiline input. Use the default one. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Jan 25, 2021 at 13:05
If you catch the exception, you will see regex_error(error_escape): The expression contained an invalid escaped character, or a trailing escape. — rustyx
– rustyx, Commented Jan 25, 2021 at 13:08
externded syntax only allows certain special characters to be escaped by a backslash, not any arbitrary character. In particular, space is not a special character, and \ is invalid in extended syntax. So are \n and \r it seems; those characters should be represented by themselves (which would be tricky in a raw string literal). All told, you probably don't want extended; you are probably looking for multiline option. — Igor Tandetnik
– Igor Tandetnik, Commented Jan 25, 2021 at 13:11

rustyx · Accepted Answer · 2021-01-25 13:28:37Z

2

According to the regex spec, the effect of escaping a space (which is not a special character) is undefined:

9.4.2 ERE Ordinary Characters

... The interpretation of an ordinary character preceded by an unescaped <backslash> ( \ ) is undefined, except in the context of a bracket expression ...

Apparently in the MSVC implementation, std::regex_error gets thrown.

After fixing the escaping the regex compiles.

try {
    std::regex regexp(
        R"(\$ part, model.*[\n\r]([-]?[0-9]*\.?[0-9]+[Ee]?[-+]?[0-9]*),([-]?[0-9]*\.?[0-9]+[Ee]?[-+]?[0-9]*))", std::regex::extended);
}
catch (std::exception const& e) {
    std::cerr << e.what() << std::endl;
}

answered Jan 25, 2021 at 13:28

rustyx

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