Dynamic memory allocation in C

Malloc ,Callloc, Realloc, free:

1)Malloc: Malloc dynamically allocates requested memory and returns pointer to it.

/* We are allocating memory for "n" integers and returns integer pointer */
int *ptr = (int *) malloc(n * sizeof(int)); // We have type casted pointer to int

2)Calloc: Calloc dynamically allocates requested memory and initializes it to zero. Calloc is compiler independent.

/* We are allocating memory for "n" integers and returns integer pointer */
int *ptr = (int *) calloc(n,sizeof(int)); // We have type casted pointer to int

3)Realloc: Realloc is used when we have dynamically allocated memory and need to resize it. Realloc can beused as a substitute to malloc or free.

(void*) realloc(void *ptr ,sizeof(int));

4)free:

After use of dynamically allocated memory, free the memory. Consider below example: int *ptr = (int *) malloc(n * sizeof(int)); //Use dynamically allocated memory

free(ptr); ptr = NULL;// NULL represents address 0 and it can not be dereferenced so ptr can not be dereferenced.