Can anyone explain me syntax of malloc ( ), calloc( ), realloc( )? And how exactly it works.

Question

I am not getting how malloc, calloc, realloc works. Please explain me in simple words as I am beginner !

Answer 1

malloc() will just reserve a contiguous block of memory (in this case 200 bytes if sizeof(int) = 4). (int*) tells the compiler that you are going to use this memory block to store integers

Answer 2

If you want to allocate memory for 50 integers using malloc(), the syntax is

int *nums = (int*)malloc(50*sizeof(int));

You know that it worked if the result is not a null pointer:

if(nums == NULL) {
// something went wrong
}

You can combine those to steps like this:

int *nums;

if((nums = (int*)malloc(50*sizeof(int))) != NULL) {
// do something with the allocated memory
} else {
// failed to allocate memory
}

calloc() basically does the same as malloc() but it will set the allocated memory to 0, and the syntax is slightly different:

int *nums = (int*)calloc(50, sizeof(int));

realloc() reallocates memory that was allocated with malloc or calloc before.

If you're running out of memory and want to reallocate memory for 50 more integers, the syntax would be

nums = realloc(nums, 100*sizeof(int));

To free the memory and avoid memory leaks, use free(nums); when you don't need the allocated memory any longer.

Answer 3

https://www.sololearn.com/learn/C/2948/

https://www.sololearn.com/learn/C/2949/

Answer 4

It is hard to me to get it !
Please explain me in simple words.*AsterisK*

Answer 5

Thanks Anna
But what is meaning of this
ptr = (int*) malloc (50*sizeof(int));
What is meaning of return type int* here.
What are the behind the scenes!