INTERVIEW QUESTIONS C DYNAMIC MEMORY ALLOCATION IN C DETAILS

Question: Difference between calloc() and malloc()?

Answer: malloc: malloc create the single block of given size by user
calloc: calloc creates multiple blocks of given size
both return void pointer(void *)so boh requires type casting
malloc: eg:
int *p;
p=(int*)malloc(sizeof(int)*5)
above syntax tells that malloc occupies the 10 bytes memeory and assign the address of first byte to P

calloc: eg:
p=(int*)calloc(5,sizeof(int)*5)
above syntax tells that calloc occupies 5 blocks each of the 10 bytes memeory and assign the address of first byte of first block to P

malloc: malloc create the single block of given size by user
calloc: calloc creates multiple blocks of given size
both return void pointer(void *)so boh requires type casting
malloc: eg:
int *p;
p=(int*)malloc(sizeof(int)*5)
above syntax tells that malloc occupies the 10 bytes memeory and assign the address of first byte to P

calloc: eg:
p=(int*)calloc(5,sizeof(int)*5)
above syntax tells that calloc occupies 5 blocks each of the 10 bytes memeory and assign the address of first byte of first block to P
Source: CoolInterview.com

the above answer is absolutely right,but the difference between calloc and malloc is that calloc also initialize the reserved memory block to zero rather than garbage value in case of malloc() Source: CoolInterview.com

Another difference is that calloc takes two arguments while malloc takes only one argument.
malloc: eg:
int *p;
p=(int*)malloc(sizeof(int)*5)
calloc: eg:
p=(int*)calloc(5,sizeof(int)*5)
Source: CoolInterview.com

malloc and calloc both are dynamic allocation of memory ie at run time

malloc
syntax:
void *malloc(size_t n);
returns a pointer of n bytes of unintialized storage and returns NULL if failed

calloc
syntax:
void *calloc(size_t n, size_t size)

returns a pointer of enough free space of array of n objects of specified size,but initialized storage with zeros,returns NULL if failed.

Note: to use pointer returned by malloc and calloc it should be type casted

Source: CoolInterview.com

malloc allocates requested memory in bytes in heap area
void *malloc(size_t size)
calloc function allocates memory for specified number of objects where size of the each object is given in the function call.eg:if we specify the number of objects as 5 n size of the each object as 5bytes then total memory allocated is 25bytes..
syntax:void *calloc(int nobj,size_t size);
for both of the functions we need not do a explicit typecasting.
on success they return address of the allocated area n on failure they return NULL. Source: CoolInterview.com

Calloc: used for reserving multiple blocks of memory.for example dynamic multi-dimensional arrays.

Memory Cannot be modified using realloc() function

Malloc:used for reserving the Single block of memory.

Memory Can be modified using realloc() function Source: CoolInterview.com

addition with the above:
I think memory allocated by malloc or calloc function can be modified through realloc function.

try below example :
void main()
{
int *p=(int*)calloc(2,sizeof(int)*2);

for(int i=0; i<4;i++)
p[i] = i;

printf("Memory allocated dynamically for 2 block each has 4 bytes:
");

for(int i=0; i<4;i++)
printf("%d
", p[i]);

realloc(p,sizeof(int)*6);

for(i=0;i<6;i++)
p[i] = i;

printf("Memory allocated dynamically for 6 bytes:
");

for(int i=0; i<6;i++)
printf("%d
", p[i]);
getchar();
} Source: CoolInterview.com

malloc():this fun is used for allocating a block of memory in bytes at runtime.It reurns void pointer.
calloc():this fun is used for allocating continous blocks of memory at runtime.This is especiaaly designed for arrays. Source: CoolInterview.com

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