C Language : Dynamic Memory Allocation (DMA)

Dynamic Memory Allocation (DMA):

Many languages permit a programmer to specify an array’s size at run time. Such languages have the ability to calculate and assign memory spaces required by the variable during run time (execution) of program. The process of allocating memory at run time is known as Dynamic Memory Allocation. In C, there are four library functions (routines) known as “Memory Management Functions” that can be used for allocating and freeing memory during program execution. We required a header file “stdlib.h” for using DMA functions in the program.

Required functions: malloc( ), calloc( ), realloc( ), free( ).

malloc( ) :- This function is used to allocate requested size of bytes and returns a void pointer to the first byte of the allocated space. We can assign it for any type of pointer.

Syntax:

            ptr=(cast-type *) malloc( byte-size);

            intPtr=(int *) malloc(5 * sizeof(int));      => allocating 10 bytes for integer.

            chPtr=(char *) malloc(12);           => allocating 12 bytes for character.

calloc( ) :- This function is used to allocate requesting memory space at run time for storing derived data types such as arrays and structures. While malloc( ) allocates a single block of storage space, calloc( ) allocates multiple blocks of storage of same size. Initializes all the bytes to zero and then returns a pointer to the memory.

Syntax:

            ptr=(cast-type *) calloc( n, element-size);

free( ) :- When we no longer need the data stored in a previously allocated memory space, then we can free that memory space dynamically at run time using this function. Here “ptr” is a pointer to a memory block which has already been created by malloc or calloc.

Syntax:

            free(ptr);

realloc( ) :- It is also possible that we can increase or reduce memory size created by malloc function. realloc( ) function is used to modify the size of previously allocated spaces. This process is called the reallocation of memory.

Syntax:

            ptr=(cast-type *) malloc(size);

            ptr=realloc(ptr, new-size);

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