[Solved] Can I access a location in vector which I haven’t declared? [duplicate]

Question

The answer can be read in the C++ reference.

Here you can read that no boundary check will be done and no new element will be inserted. You simply have undefined behaviour.

So, in moredetail:

using an index operator with an index bigger than the size of the vector, will not increase the size of the vector and add new elements.
Using an out of bound index that is bigger than the vectors size, will simply access a memory location, which does not belong to the vector.
Reading such a position will mostly give a random value or better set, an undefined value. This will usually not harm your program, except that you get undefined values back.
Writing to an out of bounds value usually is a very severe problem, because you are overwriting memory, which you do not won. Very dangerous.

If you want to have boundary checking, then use vectors at-function.

Accepted Answer

The answer can be read in the C++ reference.

Here you can read that no boundary check will be done and no new element will be inserted. You simply have undefined behaviour.

So, in moredetail:

using an index operator with an index bigger than the size of the vector, will not increase the size of the vector and add new elements.
Using an out of bound index that is bigger than the vectors size, will simply access a memory location, which does not belong to the vector.
Reading such a position will mostly give a random value or better set, an undefined value. This will usually not harm your program, except that you get undefined values back.
Writing to an out of bounds value usually is a very severe problem, because you are overwriting memory, which you do not won. Very dangerous.

If you want to have boundary checking, then use vectors at-function.