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

Introduction

This question is related to the use of vectors in programming. A vector is a data structure that stores a collection of elements, and it is often used in programming languages such as C++ and Java. The question is whether it is possible to access a location in a vector which has not been declared. This is an important question to consider when working with vectors, as accessing an undeclared location can lead to unexpected results. In this article, we will discuss the answer to this question and provide some examples to illustrate the concept.

Solution

No, you cannot access a location in a vector which you have not declared. The vector must be declared with a specific size, and you can only access elements within that size. Attempting to access an element outside of the declared size will result in an error.

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.

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

The short answer to this question is no, you cannot access a location in a vector which you have not declared. A vector is a data structure that stores elements in a contiguous memory location. This means that all elements must be declared before they can be accessed. If you try to access an element which has not been declared, you will get an error.

In order to access elements in a vector, you must first declare them. This can be done by using the vector’s constructor, which takes a list of elements as its argument. For example, if you wanted to declare a vector of integers, you could do so like this:

std::vector<int> myVector {1, 2, 3, 4, 5};

Once the vector has been declared, you can access its elements using the [] operator. For example, if you wanted to access the third element in the vector, you could do so like this:

int thirdElement = myVector[2];

In summary, you cannot access a location in a vector which you have not declared. You must first declare the elements in the vector before you can access them.