Memory Allocation for Data

When a variable is declared, enough memory to hold a value of that type is allocated for it at an unused memory location. This is the address of the variable.

For example:

int x;    //will take 2 bytes
float number;    //will take 4 bytes
char ch;   //will take 1 byte

Kinds of Memory Allocation

3 Kinds of Data in a Program

STATIC DATA: memory allocation exists throughout execution of program.
                 static long SeedValue;

AUTOMATIC DATA: automatically created at function entry, resides in activation frame of the function, and is destroyed when returning from function.

DYNAMIC DATA: explicitly allocated and deallocated during program execution by C++ instructions written by programmer using unary operators new and delete

Using new operator (dynamic data allocation)

If memory is available in an area called the free store (or heap), operator new allocates the requested object or array, and returns a pointer to (address of ) the memory allocated.

Otherwise, the null pointer is returned.

The dynamically allocated object exists until the delete operator destroys it.

Next

Using delete operator (dynamic data de-allocation)

The object or array currently pointed to by the pointer is deallocated, and the pointer is considered unassigned. The memory is returned to the free store.

Another example - Dynamic Array Allocation

Reallocation

Memory Leak

A memory leak occurs when dynamic memory (that was created using operator new) has been left without a pointer to it by the programmer, and so is inaccessible.