Pattern Matching on every element in the vector

Question

I have a function which looks like this:

bool ExpandWildCard(vector<string>& names, vector<string>& result, string& wildcard) 
{
}

Here, I want to match the wildcard with each element in the vector names and if it does match, then add the element in names to the result vector.

Of course, if the wildcard is *, I could just add everything from names to results. Also I'm just trying to implement the * wildcard for now.

How can I do this in C++?

One way I thought of doing this was using find() algorithm but I am not sure I would match wildcards using that?

do you want to do full regular expression matching? see `std::regex` — TemplateRex, Aug 04 '14 at 14:07
This question is not too broad, it is clearly about how to do glob match. — jxh, Aug 04 '14 at 17:17

Arne Mertz · Accepted Answer · 2014-08-05T06:25:04.393

It looks like you are looking for some combination of std::copy_if and maybe std::regex_match:

bool ExpandWildCard(vector<string>& names, vector<string>& result, string& wildcard) {
  auto oldsize = result.size();
  std::copy_if(std::begin(names), std::end(names),
    std::back_inserter(result),
    [&](string const& name) {
      return std::regex_match(name, make_regex(wildcard));
    }
  );

  return (result.size() > oldsize);
}

Where make_regex would be the function you need to implement to convert your string into a std::regex.

score 0 · Answer 2 · edited May 23 '17 at 12:11

The approach you are probably after in using regex_match as suggested in another answer. Elsewhere you can find code to convert a glob pattern into a regular expression.

If performance is not a concern, and you just need the functionality, you can use the shell to match the pattern for you. You can create a suitable command, pass the command through popen() and read the results and store them in your vector.

bool ExpandWildCard (const std::vector<std::string>& names,
                     std::vector<std::string>& result,
                     const std::string& wildcard)
{
    std::ostringstream oss;
    oss << "bash -c 'for word in ";
    for (int i = 0; i < names.size(); ++i) {
        if (names[i].size() > 0) oss << '"' << names[i] << '"' << ' ';
    }
    oss << "; do case \"$word\" in "
        << wildcard << ')' << " echo \"$word\" ;; *) ;; "
        << "esac ; done '";
    FILE *fp = ::popen(oss.str().c_str(), "r");
    if (fp == NULL) return false;
    char *line = 0;
    ssize_t len = 0;
    size_t n = 0;
    while ((len = ::getline(&line, &n, fp)) > 0) {
        if (line[len-1] == '\n') line[len-1] = '\0';
        result.push_back(line);
    }
    ::free(line);
    ::pclose(fp);
    return true;
}

Pattern Matching on every element in the vector

2 Answers2