Why is a variable declared in a local scope, and put into a vector visible outside the scope?

Question

My question is in regard to the following piece of code:

pairVectors.push_back(new vector<CompactPair>());

for (int i = 0; i < generationVectors[0].size(); ++(i))
{
    //Find the new indices of the two symbols in this pair
    long leftIndex = ((terminalIndices)[(generationVectors[0])[i].leftSymbol]);
    long rightIndex = ((terminalIndices)[(generationVectors[0])[i].rightSymbol]);

    //Make a pair out of the indices we found, then push it to the vector
    CompactPair p(leftIndex, rightIndex);
    pairVectors[0]->push_back(p);


    //Record the index of this symbol
    if (indices[(generationVectors[0])[i].leftSymbol].empty())
    {
        indices[(generationVectors[0])[i].leftSymbol].set_empty_key(-1);
        indices[(generationVectors[0])[i].leftSymbol].set_deleted_key(-2);
    }
    ((indices)[(generationVectors[0])[i].leftSymbol])[(generationVectors[0])[i].rightSymbol] = i + terminals.size();
}

The CompactPair p is created using the following constructor:

CompactPair::CompactPair(long left, long right)
{
    leftSymbol = left;
    rightSymbol = right;
}

Whether or not it is being pushed onto the vector does not seem to matter, leftIndex, rightIndex, p and i all remain visible outside the scope of the loop. Can anybody explain this?

I'm using the Intel c++ 15.0 compiler with optimizations disabled.

Answer 1

You are inserting fully constructed object in your vector so when calling push_back , you are effectively copying(or moving if enabled) the object to a new one which sits in the vector. The scope of this new object is then tied to the one of the vector.