Stack or Heap: Where Does a C Vector Store Its Memory?

Memory Allocation in Vectors

In C , vectors are used to store a collection of elements. Depending on how vectors are declared and initialized, memory for the vector and its elements can be allocated either on the stack or the heap.

Stack Allocation vs Heap Allocation

The stack is a memory segment used for storing function local variables and arguments. It grows towards lower memory addresses. In contrast, the heap is another memory segment used for dynamically allocated memory. It grows towards higher memory addresses.

Vector Declaration and Memory Allocation

In the following statement, the vector vect is allocated on the stack along with its elements:

vector<Type> vect;

However, in this statement, the pointer vect is allocated on the stack, but the vector itself and its elements are allocated on the heap:

vector<Type> *vect = new vector<Type>;

Finally, in this statement, the vector vect is allocated on the stack, while the pointers it contains are allocated on the heap:

vector<Type*> vect;

Memory Allocation for Elements in STL Containers

In general, for STL containers such as vectors, the memory for the container itself is allocated on the stack. However, the memory for the elements stored in the container is managed dynamically and is typically allocated on the heap. This allows the container to grow and shrink in size as needed.

Therefore, the memory allocation for vectors and other STL containers is managed carefully to optimize performance and memory usage. By understanding how memory allocation works in vectors, programmers can optimize their code and make efficient use of system resources.

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