CODEWITHSUNDEEP
c++dictionarystliterator
user2512322
user2512322

Reputation: 25

Check if map contains all the keys from another map

Check if map in C++ contains all the keys from another map answers my question but I'm not sure how we iterate through two maps at the same time.

I know how to iterate through one as shown:

typedef std::map<QString, PropertyData> TagData;
TagData original = readFileToMap("FoxHud.bak");

for (TagData::const_iterator tagIterator = original.begin(); tagIterator != original.end(); tagIterator++) {
}

Upvotes: 2

Views: 627

Answers (2)

Yohan Danvin
Yohan Danvin

Reputation: 910

If you want to iterate the 2 maps simultaneously, you can do this:

if (map1.size() != map2.size())
  ; // problem
else
{
  for (map<X,Y>::const_iterator it1 = map1.begin(),
                                it2 = map2.begin();
       it1 != map1.end() && it2 != map2.end();
       ++it1 , ++it2)
  {
    // ...
  }
}

Now if you want to iterate through the 2 maps at different "speeds", then a while loop to condition the increments of it1 and it2 independently would then be more appropriate. See Golgauth's answer for an example.

Upvotes: 0

Gauthier Boaglio
Gauthier Boaglio

Reputation: 10272

Try this way:

// As std::map keys are sorted, we can do:

typedef std::map<string, int> TagData;
TagData map1;
TagData map2;
...
TagData::const_iterator map1It = map1.begin();
TagData::const_iterator map2It = map2.begin();

bool ok = true;
std::size_t cnt = 0;

while (map2It != map2.end() && map1It != map1.end()) {
    if (map1It->first != map2It->first) {
        map1It++;
    } else {
        map2It++;
        cnt++;
    }
}

if (cnt != map2.size()) ok = false;

cout << "OK = " << ok << endl;

This should work with maps that are not the same size, as well.

Upvotes: 2

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