Find values in vector within map< string, <vector<string> > in c++

Question

std::map< std::string, std::vector<std::string> > families;

// add new families
families["Jones"];
families["Smith"];
families["Doe"];

// add children
families["Jones"].push_back( "Jane" );
families["Jones"].push_back( "Jim" );

I added the values to vector within the map using above method. How can I check if "Jane" exists in map with key "Jones"?

Answer 1

Use the find member function of std::map for this and after that a regular string search:

std::map<std::string, std::vector<std::string> >::const_iterator search = families.find("Jones");
if(search != families.end()) 
{
  std::vector<std::string> s = search->second;
  if (std::find(s.begin(), s.end(), "Jane") != s.end())
  {
  }
}

Answer 2

Here's an example:

#include <iostream>
#include <string>
#include <map>
#include <vector>
#include <algorithm>

int main()
{
    std::map< std::string, std::vector<std::string> > families;

    // add new families
    families["Jones"];
    families["Smith"];
    families["Doe"];

    // add children
    families["Jones"].push_back( "Jane" );
    families["Jones"].push_back( "Jim" );

    auto family_iterator = families.find("Jones");
    if (family_iterator != families.end())
    {
        const std::vector<std::string>& family = family_iterator->second;
        if (std::find(family.begin(), family.end(), "Jane") != family.end())
            std::cout << "found\n";
    }
}

Basically, families.find() searches in a map and returns an iterator , for which ->first is the key you've found and ->second is the value: your value is the std::vector<std::string> for the "Jones" family, and for convenience/concision I create a const reference to it.

To search in vector I use std::find() from <algorithm> .

Code available/runnable here

Answer 3

Just check if given surname is in your map and then use std::find . I am not using auto , as from the comments I believe you may not be using C++11-compatible compiler.

#include <map>
#include <vector>
#include <iostream>
#include <algorithm>

bool exists(std::map<std::string, std::vector<std::string> >& families,
            std::string& name, std::string& surname) {
    if(families.find(surname) == families.end()) return 0;
    std::vector<std::string> names = families[surname];
    return std::find(names.begin(), names.end(), name) != names.end();
}

int main(int argc, char* argv[]) {
    std::map<std::string, std::vector<std::string> > families;

    // add new families
    families["Jones"];
    families["Smith"];
    families["Doe"];

    // add children
    families["Jones"].push_back("Jane");
    families["Jones"].push_back("Jim");

    std::string name("Jane"), surname("Jones");
    bool ex1 = exists(families, name, surname);
    std::cout << ex1 << std::endl;

    return 0;
}