如何使String :: Find（is）省略

Question

If I have a list, which contains the 4 nodes ("this"; "test example"; "is something of"; "a small") and I want to find every string that has "is" (only 1 positive with this list). This topic has been posted a large number of times, which I have used to help get me this far. However, I can't see anywhere how I omit "this" from a positive result. I could probably use string::c_str, then find it myself, after I've reduced my much larger list. Or is there a way I could use string::find_first_of? It would seem there's a better way. Thanks.
EDIT: I know that I can omit a particular string, but I'm looking for bigger picture b/c my list is quite large (ex: poem).

for(it = phrases.begin(); it != phrases.end(); ++it)
{
    found = it->find(look);
    if(found != string::npos)
        cout << i++ << ". " << *it << endl;
    else
    {
        i++;
        insert++;
    }
}

Answer 1

Just to clarify: what are you struggling with?

What you want to do is check if what you have found is the start of a word (or the phrase) and is also the end of a word (or the phrase)

ie. check if:

• found is equal to phrases.begin OR the element preceding found is a space
• AND two elements after found is a space OR phrases.end

EDIT: You can access the character that was found by using found (replace X with the length of the string you're finding (look.length)

found = it->find(look);
if(found!=string::npos)
{
    if((found==0 || it->at(found-1)==' ')
        && (found==it->length-X || it->at(found+X)==' '))
    {
         // Actually found it
    }
} else {
    // Do whatever
}

Answer 2

I didn't realize you only wanted to match "is". You can do this by using an std::istringstream to tokenize it for you:

std::string term("is");

for(std::list<std::string>::const_iterator it = phrases.begin();
    it != phrases.end(); ++it)
{
    std::istringstream ss(*it);
    std::string token;
    while(ss >> token)
    {
        if(token == term)
            std::cout << "Found " << token << "\n";
    }
}

Answer 3

We can use boost regex for searching regular expressions. Below is an example code. Using regular expression complex seacrh patterns can be created.

#include <boost/regex.hpp> 
#include <string> 
#include <iostream> 
#include  <boost/tokenizer.hpp>

using namespace boost;
using namespace std;

int main()
{
  std::string list[4] = {"this","hi how r u ","is this fun is","no"};

  regex ex("^is"); 

  for(int x =0;x<4;++x)
  {
    string::const_iterator start, end;
    boost::char_separator<char> sep(" ");
    boost::tokenizer<boost::char_separator<char> > token(list[x],sep);

    cout << "Search string:  " << list[x] <<"\n"<< endl;
    int x = 0;
    for(boost::tokenizer<boost::char_separator<char> >::iterator itr = token.begin();
        itr!=token.end();++itr)
    {
      start = (*itr).begin();
      end = (*itr).end();

      boost::match_results<std::string::const_iterator> what;
      boost::match_flag_type flags = boost::match_default;

      if(boost::regex_search(start, end, what, ex, flags))
      {
        ++x;
        cout << "Found--> " << what.str() << endl;
      }
    }

    cout<<"found pattern "<<x <<" times."<<endl<<endl;
  }
  return 0;
}

Output:

Search string: this

found pattern 0 times.

Search string: hi how ru

found pattern 0 times.

Search string: is this fun is

Found--> is Found--> is found pattern 2 times.

Search string: no

found pattern 0 times.