CODEWITHSUNDEEP
c++dictionaryfind
vincentdj
vincentdj

Reputation: 265

map with vector as key operation find

I have a:map<vector<int>, vector<int>> info

I have to do a search. I try: 

Key[0]=1;
Key[1]=3;
Key[2]=1;
test=info.find(key);

Where Key and test are defined as follows:vector<int> Key (3,0) and vector<int> test (2,0).

But this returns a compilation error: error: no match for 'operator=' in 'test =. What is the reason for this?

Upvotes: 1

Views: 5233

Answers (2)

Felix Glas
Felix Glas

Reputation: 15524

You get the error because std::vector does not have an operator overload for iterator assignment.

std::vector<int>::find returns an input iterator. std::vector<int>::operator= takes another std::vector<int> or a C++11 initializer-list.

You should try something like this instead.

// Some map.
std::map<std::vector<int>, std::vector<int>> info{ { { 1, 3, 1 }, { 5, 5, 5 } } };

auto itr = info.find({ 1, 3, 1 }); // Find element
if (itr != std::end(info)) {       // Only if found
    auto& v = itr->second;         // Iterator returns std::pair (key, value)
    for (auto i : v) {             // Print result or do what you want.
        std::cout << i << std::endl;
    }
}

Upvotes: 0

Benjamin Lindley
Benjamin Lindley

Reputation: 103693

find returns an iterator. First you need to check if the key was actually found, by testing it against info.end(). Then, you need to assign from the value, which is stored in the second of the pair.

auto it = info.find(key);
// pre-c++11: std::map<vector<int>, vector<int> >::iterator it = info.find(key)
if (it != info.end())
{
    test = it->second;
}

Upvotes: 4

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