STL container questions

[Allerdyce.John]

Hi,

What will happen if i access an element which is bigger than the
container?
e.g.
vector<int> aVector(1);
cout << aVector[6] << endl?
// or can I do this:
aVector[6] = 3;

How about a Map?
map<int, int> aMap(1);
aMap[2] = 1;
aMap[1] = 2;

 

[Ben Pope]

Hi,

What will happen if i access an element which is bigger than the
container?
e.g.
vector<int> aVector(1);
cout << aVector[6] << endl?

/the above line causes undefined behaviour, ANYTHING could happen from
now one.

// or can I do this:
aVector[6] = 3;

//Same as above

How about a Map?
map<int, int> aMap(1);
aMap[2] = 1;
aMap[1] = 2;

No, they are both fine, assuming you remove the UB above.

What book are you reading that does not discuss this?

Ben Pope

 

[Victor Bazarov]

What will happen if i access an element which is bigger than the
container?

Usually the behaviour is undefined. If you use .at() instead of
the indexing, then 'vector' throws and you can catch the exception.

e.g.
vector<int> aVector(1);
cout << aVector[6] << endl?
// or can I do this:
aVector[6] = 3;

The behaviour is undefined.

How about a Map?
map<int, int> aMap(1);
aMap[2] = 1;
aMap[1] = 2;

'std::map' actually inserts if the element doesn't exist.

V