C ++ regex_search捕获检索在运行时失败

Question

I'm following an example in Stroustrup's Tour of C++ - section 7.3.1 (page 79). This code compiles on VS 2013 Update 3 but fails at runtime:

regex pat {R"(\w{2}\s+(\d{5}))"};
smatch matches;
if (regex_search(string{"CA 90210"}, matches, pat))
{
    if ((matches.size() > 1) && matches[1].matched)
    {
        cout << matches[1] << endl;
    }
}

Any idea what is going on? It fails on matches[1] where I'm trying to output the capture group result to stdout. The runtime assertion I see is "string iterators incompatible".

Answer 1

smatch object contains iterators into the string you searched with the regular expression. Said string is a temporary in your example, and is dead by the time you are trying to inspect the matches. All those iterators are dangling.

Make it

string s = "CA 90210";
if (regex_search(s, matches, pat)) {...}