C Programming - Pointers - Discussion

Can anybody explain where is the pointer use, what is the purpose using of pointer?

Actually return type of malloc() or calloc() void pointer. So should typecast it.

If p is a pointer.

i.e. p addressing some variable for eg x.

The p stores the address of x.

And *p gives the value of x. Is this correct or not?

char *p;

Here *p means value of p.

And p= (char *) malloc (1000); which is saying that value of p is char*..

Therefore,

They can be combined as:

char *p = (char *) malloc (1000);

Say: int a=10;

// This means a is a variable where 10 is stored.

Now say the address/ memory location of a is 5000.

So, I say: int *a= 5000;

// 5000 refers to the memory location of a or pointed to a.

Hence

For storing a value you need a definition statement and for storing a memory address you need a pointer.

Here the memory is allocated by malloc function. P is local variable so the memory is allocated on stack for P. But the memory allocated by malloc function is 100 byte and which is allocated on HEAP. Here the type of pointer is character so for allocating the memory malloc is type casted with character, Because malloc always returns void*.

So void* is a pointer which pointing to particular address but can not access the element from that address. For allocating memory malloc internally call sbrk and brk algorithm. This algorithm internally called by growrage algorithm.

#include<stdio.h>
int main(){
int i=320;
char *ptr=(char*)&i;
printf("%d",*ptr);
return 0;
}

Ans: 64.

Could anyone explain this program and answer?.

1. char p;
p= (char *) malloc (1000) ;

2. char *p;
p= (char *) malloc (1000) ;

Is that 1 and 2 mean the same. explain?

malloc & calloc both are memory allocation function & both returns void type where afterwords we type case it.

ex:

int *p;
p=(int*)malloc(1000);

where malloc depends upon byte which are fixed i.e 8-bit,again 16-bit.

calloc deals with no.of bytes where bytes is considered as block relevant to the memory issue.

Please can an one explain malloc and calloc function ?