CODEWITHSUNDEEP
c++data-structuresunordered-map
jpb123
jpb123

Reputation: 335

How to use unordered_map of unordered_maps in c++?

I have below data structures problem ? Could you please help me out. So I my requirement is to initialise this data structures to default values when I add the new data items into this map.

How can I do this efficiently ?

I need a1, a2, a3 should be set to zero for each entry I am going to add. 

struct a {
 int a1;
 int a2;
 int a3;
};

struct A {
 struct a A1;
 struct a A2;
};

unordered_map<int, unordered_map<int, struct A>> big_map;

Tried running below code.

    unordered_map<int, struct A> inner_map;
    big_map[0] = inner_map;
    struct A m;
    big_map[0][0] = m;
    cout << "Values: " << big_map[0][0].A1.a1 << ", " << big_map[0][0].A1.a2 << ", " << big_map[0][0].A1.a3 << endl;

Output:

g++ -std=c++11 -o exe b.cc ./exe Values: 0, 0, 1518395376 ./exe Values: 0, 0, -210403408 ./exe Values: 0, 0, -1537331360 ./exe Values: 0, 0, -915603664

So default initialisation is not being done for a3 ?

Upvotes: 3

Views: 163

Answers (3)

Slava
Slava

Reputation: 44278

Since C++11 you can do this:

struct a {
 int a1 = 0;
 int a2 = 0;
 int a3 = 0;
};

Upvotes: 6

physicist
physicist

Reputation: 904

You can give constructor to struct just like class, and init it to 0

struct a
{
   int a1;
   int a2;
   int a3;
   a() : a1(0), a2(0), a3(0)
   {
   }
}

Upvotes: 2

scohe001
scohe001

Reputation: 15446

You can add a default constructor to your structs:

struct a {
    a() : a1(0), a2(0), a3(0) { }
    ...
};

struct A {
    A() : A1(), A2() { }
    ...
};

And then when you add a new struct you can do:

big_map[5][7] = A();

Upvotes: 2

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