Question

The Vector find function can search an inserted value even if you try and find by providing substring . Is this same in case of the keys of a map ?

   int main()
   { 
    vector<string> v;
    v.push_back("text");
    v.push_back("[[text");
    v.push_back("text");

    for (unsigned i = 0; i < v.size(); i++)
     {
       if (v[i].find("[[") == 0)
       {
         v[i].append("]]");
       }
     }
  }

Here it finds “[[text” and makes it “[[text]]” .

I tried it in map but code crashes on run time ,. I am using Dev c++

   int main()
{
      std::multimap<string, string> m;
      std::multimap<string, string> intersection;
      std::multimap<string, string>::iterator it8;

      m.insert(pair< string, string>("4-2"," 61-7" ));
      m.insert(pair< string, string>("5-2"," 61-7" ));

     multimap<string, string>::iterator it4;
     multimap<string, string>::iterator it5;
    for ( it4 = m.begin(); it4 !=m.end(); it4++)
    {
        if (m.find("5-") == 0)
        it5=it4;      
    }
    cout << " result of 5 search is" << (*it5).first << ", " << (*it5).second <<endl;
    m.clear();
   getchar();

 }

Answer 1

(Sample correct code on ideone)

The error is that this line

if (m.find("5-") == 0)

will never succeed. You maybe be surprised at this. m.find("5-") searches through the entire map looking for an entry whose key is exactly equal to “5-“. Your keys are “4-2” and “5-2”.

Do you wish to find keys which contain the substring “5-“? Then you need something like

it4->first.find("5-"); // check if the key string at this entry contains "5-"

I think you want a loop like this:

multimap<string, string>::iterator it4;
for ( it4 = m.begin(); it4 !=m.end(); it4++)
{
    if (it4->first.find("5-") != string :: pos)
            cout << " result of 5 search is" << it4->first << ", " << it4->second <<endl;      
}

As others have pointed out, you are not interested in the the find method of vector or map. You are interested in the find method of string – this is quite different. The title of your question is a little misleading as a result (unintentionally).