CODEWITHSUNDEEP
c++dictionary
MrDuk
MrDuk

Reputation: 18242

Why does my map of maps print all zeros?

I'm doing the following:

//d = 3701
//h = 3702
//c = 8
map<int, map<int,int> > table;
table[d][h] = c;
table iter = table.begin(); 
while(iter != table.end())
{
    cout << "d: " << iter->first << "h: " << iter->second[0] << "c: " << iter->second[1] << endl;
    iter++;
}

But my output is showing: d: 3701 h: 0 c: 0

Upvotes: 0

Views: 117

Answers (1)

4pie0
4pie0

Reputation: 29724

The only element on this map is with key = 3701 and this is a map which has only 1 element with key 3702, equal to 8. If you try to access any other element like

iter->second[0] // inner map has no key = 0, so key = 0 with default value 
                // assigned to it is created

iter->second[1] // inner map has no key = 1, so key = 1 with default value 
                // assigned to it is created

std::map will insert default value to it.

If you want do avoid insertion of default values when checking if they are present you shoud use find() function to compare with map.end() iterator.

while( iter != table.end())
{
    cout << "d: " << iter->first;
    if ( (iter->second).find(0) != (iter->second).end())
         cout << "key 0, value: " << iter->second[0] << endl;
    ++iter;
}

Upvotes: 2

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