map of vectors in STL?


Question

I want to have a map of vectors, (but I don't want to use pointer for the internal vector), is it possible?

// define my map of vector
map<int, vector<MyClass> > map;

// insert an empty vector for key 10. # Compile Error
map.insert(pair<int, vector<MyClass> >(10, vector<MyClass>)); 

I know that if I have used pointer for vector, as follows, it would be fine, but I wonder if I can avoid using pointer and use the above data structure (I don't want to manually delete)

// define my map of vector
map<int, vector<MyClass>* > map;

// insert an empty vector for key 10.
map.insert(pair<int, vector<MyClass>* >(10, new vector<MyClass>)); 
1
24
9/4/2009 5:40:06 PM

Accepted Answer

The first data structure will work. You might want to typedef some of the code to make future work easier:

typedef std::vector<MyClass>      MyClassSet;
typedef std::map<int, MyClassSet> MyClassSetMap;

MyClassSetMap map;
map.insert(MyClassSetMap::value_type(10, MyClassSet()));

or (thanks quamrana):

map[10] = MyClassSet();
30
5/23/2017 12:02:26 PM

Yes, but your second line should be:

map.insert(pair<int, vector<MyClass> >(10, vector<MyClass>()));

This inserts a pair consisting of the integer 10, and an empty vector. Both will be copied, and if you're dealing with large vectors then you'll want to be careful about copies.

Also: don't call variables "map" while using namespace std. You're scaring me ;-)


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