Before jumping to Dynamic memory allocation we need to know about how the memory is used by a program in C.
There are 4 memory segments :-
Stack - it is a region of limited amount of memory that is temporary allocated to a program by the processor and the compiler
It operates in LIFO (Last in first out) format. That means that the last piece of data added to the stack is the first one to be removed.
The stack is mainly used for storing local variables, function parameters and return addresses.
Heap - It is a region of memory which is used for dynamic memory allocation.
this allows more flexible memory usage, as its size is much larger than stack. So the memory can be allocated and freed in any order.
The heap is used for variables that need to persist beyond the scope of a function or for large data structures that exceed the stack's capacity.
Static/Global - The static and Global variables are stored in this part..
Code - This part of memory stores the executable code of the program.
Now back to Dynamic memory allocation…
Dynamic memory allocation refers to the process of dynamically allocating memory during runtime of a program, rather than at compile-time, i.e. static memory allocation.
By default, a limited amount of memory is allocated to a program. The default Memory allocation differs every time. It is decided by the processor and the compiler that how much memory should be allocated to a program.
In C language, Dynamic memory allocation can be done by the following functions which are present in the <stdlib.h> header file.-
malloc() -
it stands for “Memory Allocation”.
This function is used to dynamically allocate a block of memory of specified size from the heap and returns a pointer to the address of the first byte of the allocated memory in the stack.
The memory allocated using malloc() function remains in the heap untill its manually freed with the free() function.
In case, if the malloc() function is unable to allocate memory it will return NULL.
calloc() -
It stands for “Clear Allocation”.
The calloc() function is similar as the malloc() function, but with a additional feature of initializing the allocated memory block to zero.
This function is commonly used when initializing arrays or structures to avoid unpredictable behavior caused by uninitialized values.
realloc() -
It stands for “Reallocate”.
It is used to resize of memory block that was previously allocated using malloc() or calloc() functions.
If there is enough space to expand the block, the realloc() function will adjust the size of the block and return a pointer to the new memory. If there is not enough space, the function may allocate a new block of the requested size, copy the contents of the old block to the new block, and free the old block.
free() -
This function is used to deallocate memory that was previously allocated using either malloc(), calloc(), or realloc().
If a program attempts to access freed memory, it can result in undefined behavior, including crashes and unexpected results.
Syntax of the above functions…..
