dynamic memory allocation in c programming

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Explain Dynamic Memory Allocation with malloc(), calloc(), reallc(), And free() function in C example with source code

Dynamic Memory Allocation

Or

Explain malloc(),calloc(),reallc(),

And free() function in C

         In dynamic memory management memory will be allocate at runtime. This is also known as  heap memory. Some language at the run time have ability to calculate and assign the memory space at run time for an array but c can't have this feature. But in C there is some function which provide the facility to allocate and deallocate the memory. In ,Local Memory, when these function will call memory will allocate automatically and when function will exit memory will deallocated automatically . In dynamic memory allocation ,allocation of memory is explicitly requested for a  particular size of block .For deallocation of memory explicitly requested.

the function through which the dynamic memory allocation and deallocation will performed are :

1. malloc()
2. calloc()
3. free()
4. realloc()

malloc():malloc()function allocate a block of byte of memory in byte. In this when the memory block needed explicitly requested. The malloc() function is same as a function is request for RAM in the system  memory. If the request is grant then a void pointerreturn and the pointer point start of that block. If the request fail then a NULL pointer return.

Example:

malloc( number of element * size of each element);

int * ptr;

ptr = malloc(10*sizeof(int));

Where size represents the memory required in bytes .The memory which is provided is contiguous memory. But malloc function return void pointer so it needed type casting of that pointer.

Examlpe:

(type cast)malloc( number of element * size of each element);

int * ptr;

ptr =(int*) malloc(10*sizeof(int));

similarly for allocation of memory to a structure variable :

Examlpe:

(struct name)malloc( sizeof(struct name));

struct employee

{

            intemp_id;

            charemp_name[20];

            floatemp_contact_no;

};

struct employee *ptr

ptr=(struct employee*)malloc(sizeof(struct employee));

2.calloc():In malloc requested memory is provided a block of contiguous memory .calloc() function  is similar to the malloc rather then calloc() function

allocated the memory block for an array of elements. Memory for a group of objects used calloc() function. If calloc() function is executed succesfully then its allocated memory  is set as zero and a pointer  returned and if the function failed then a NULL pointer return.

Example:

void *calloc(size_tnumber,size_t size);

size_t used for unsigned on most compilers.The number is the number of objects which is allocate, and size is the size (in bytes) of each object.

int main ()

 {

intnumber,i;                

printf("Enter the number ");      

scanf("%d",&number);  

printf("Number which is here are",number);       

int *ptr = (int *) calloc (number,sizeof(int));       

for (i=0; i

{               

ptr[i] = i +i;

  }

for (i=0; i

{              

printf("Result is %d %d\n",i,ptr[i]);

 }

}

3. free ():
For deallocation of the memory which is allocated through the malloc() function and calloc() function used free() function.

Example:

free(ptr);
int main () {
      intnumber,i;
      printf("Enter the number ");
      scanf("%d",&number);
       printf("Number which is here are",number);
    for (i=0; i                                      ptr[i] = i +i;
                                     }                      for (i=0; i
                                       printf("Result is %d %d\n",i,ptr[i]);
                            }
     free(ptr);}

4.realloc()

realloc() function is used  for resize the size of memory block which is allocated by the malloc() and calloc () function.

Two situation where use realloc() function.               

·         When allocated block is insufficient need more memory then use realloc().

·         When allocated memory is much more then the required application then use realloc(). Example:

realloc(ptr, new size);

/* Through realloc() resize the memory . */

 #include

#include

#include

  {  char buffer[80], *msg;

    /* Input a string. */   

puts("Enter the text line");   

gets(buffer);

     /* The string copied in to initial allocated block */       

msg = realloc(NULL, strlen(buffur)+1);       

strcpy(msg, buffer);     

     /* Display the message which copied. */

puts(message);

       /* Get another string from the user. */    

puts("Enter another text line.");    ;

 gets(buffer);

     /* Resize the memory and also concatenate the string to it. */

   

msg = realloc(msg,(strlen(msg) + strlen(buffer)+1));    

        

strcat(msg, buffer);

     }

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