C++ regex match, not matching

Question

So I have the following text in a std::string:

2: enp1s0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc fq_codel state DOWN mode DEFAULT group default qlen 1000\    link/ether 68:f7:28:4e:7b:ac brd ff:ff:ff:ff:ff:ff

and I am trying to extract the 'enp1s0' and '68:f7:28:4e:7b:ac' using the following regex:

\d{1}:\s+(\w+).*link\/ether\s{1}([a-z0-9:]+)

which works in an online regex tester, but this C++ code does not detect a match:

std::regex interface_address("^\\d{1}:\\s+(\\w+).*link\\/ether\\s{1}([a-z0-9:]+)");
std::smatch pieces;
if (std::regex_match(line, pieces, interface_address)) {
    std::string name = "";
    std::string address = "";
    for (size_t i = 0; i < pieces.size(); ++i) {
        auto submatch = pieces[i];
        if (i == 0) {
            name = submatch.str();
        } else if (i == 1) {
            address = submatch.str();
        }
    }
    std::cout << name << address << std::endl;
}

where am i going wrong?

FYI, there's never any reason for {1} in a regexp. That's the default for any pattern. — Barmar
– Barmar, Commented Aug 21, 2016 at 3:13
What's your compiler? Not all compilers support regex well — for_stack
– for_stack, Commented Aug 21, 2016 at 3:14
Note that the name should be in pieces[1] and address is in pieces[2]. pieces[0] is the match for the entire regexp. — Barmar
– Barmar, Commented Aug 21, 2016 at 3:32

Bruno Ferreira · Accepted Answer · 2016-08-21 08:44:33Z

1

The regex_match fails when the string doesnt match EXACTLY the pattern. Note that the brd ff:ff:ff:ff:ff:ff part of the string isnt being matched. All you need to do, then, is to append a .* to the pattern:

^\\d{1}:\\s+(\\w+).*?link\\/ether\\s{1}([a-z0-9:]+).*

Also, for that example, the loop isnt necessary. You can use:

if (std::regex_match(line, pieces, interface_address)) {
    std::string name = pieces[1];
    std::string address = pieces[2];
    std::cout << name << address << std::endl;
}

edited Aug 21, 2016 at 8:44

answered Aug 21, 2016 at 8:28

Bruno Ferreira

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