Dynamic Memory Allocation in C using malloc( ),calloc( ),free( )
Dynamic Memory Allocation :
Malloc ( ) : The function most commonly used for dynamic memory allocation is malloc ( ). The prototype of the function is given below –
void * malloc (size_+size)
Malloc ( ) returns a pointer to space for an object of size, or null if the request cannot be satisfied.
The syntax is the function is given below –
x = (int*)malloc(hundred * size of (int));
On successful execution of this statement, a memory space equivalent to ‘hundred times the size of an int’ bytes is reserved and the address of first byte of the memory allocated is assigned to the pointer x of type of int.
Calloc ( ) : Calloc ( ) is another memory allocation function that is normally used for requesting memory space at run time for storing derived data types such as arrays and structures. While malloc allocates a single blog of storage place, calloc allocates multiple blocks of storages, each of the same size and then sets all bytes to zero.
General Form :
ptr = (cast_type *)calloc(n = elen_size);
The above statement allocates contiguous space for n blocks, each of size elen_size bytes. All bytes are initialize to zero and a pointer to the first byte of the allocated resin is returned. If there is not enough space, a null pointer is return.
Free ( ) : Compile time storage of a variable is allocated and released by the system in accordance with its storage class with the run time allocation, it is our responsibility to relies the space , when it is not required. The relies of storage space becomes important when the storage is limited.
When we no longer need the data we store in a block of memory and we do not intend to use that block for storing any other information, we may relies that block of memory for future use, using the free ( ) function.
Example :
free (ptr);
Where ptr is the pointer to a block of memory, which has been allocated from the heap on request. This function is void in nature and does not returned anything.
Re – alloc ( ): When the previously allocated memory is not sapient and we need additional space for more elements. It is also possible that the memory allocated is much larger then necessary and we want to reduce it. In both the cases we can change the memory size already allocated with the help of function re – alloc.
This process is called re – allocation of memory.
Example :
ptr = malloc (size);
ptr = realloc (ptr,new size);
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