如何在一个字符串中搜索多个子字符串

Question

I need to check a short string for matches with a list of substrings. Currently, I do this like shown below ( working code on ideone )

bool ContainsMyWords(const std::wstring& input)
{
    if (std::wstring::npos != input.find(L"white"))
        return true;
    if (std::wstring::npos != input.find(L"black"))
        return true;
    if (std::wstring::npos != input.find(L"green"))
        return true;
    // ...
    return false;
}


int main() {
  std::wstring input1 = L"any text goes here";
  std::wstring input2 = L"any text goes here black";

  std::cout << "input1 " << ContainsMyWords(input1) << std::endl;
  std::cout << "input2 " << ContainsMyWords(input2) << std::endl;
  return 0;
}

I have 10-20 substrings that I need to match against an input. My goal is to optimize code for CPU utilization and reduce time complexity for an average case. I receive input strings at a rate of 10 Hz, with bursts to 10 kHz (which is what I am worried about).

There is agrep library with source code written in C, I wonder if there is a standard equivalent in C++. From a quick look, it may be a bit difficult (but doable) to integrate it with what I have.

Is there a better way to match an input string against a set of predefined substrings in C++?

Answer 1

The best thing is to use a regular expression search, if you use the following regular expression:

"(white)|(black)|(green)"

that way, with only one pass over the string, you'll get in group 1 if a match was found for the "white" substring (and beginning and end points), in group 2 if a match of the "black" substring (and beginning and end points), and in group 3 if a match of the "green" substring. As you get, from group 0 the position of the end of the match, you can begin a new search to look for more matches, and everything in one pass over the string!!!

Answer 2

You could use one big if, instead of several if statements. However, Nathan's Oliver solution with std::any_of is faster than that though, when making the array of the substrings static (so that they do not get to be recreated again and again), as shown below.

bool ContainsMyWordsNathan(const std::wstring& input)
{
    // do not forget to make the array static!
    static std::wstring keywords[] = {L"white",L"black",L"green", ...};
    return std::any_of(std::begin(keywords), std::end(keywords),
      [&](const std::wstring& str){return input.find(str) != std::string::npos;});
}

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PS: As discussed in Algorithm to find multiple string matches :

The "grep" family implement the multi-string search in a very efficient way. If you can use them as external programs, do it.