how can i know the allocated memory size of pointer variable in c [duplicate]

Answer 1

You cannot use the sizeof in this case, since p is a pointer, not an array, but since you allocate it, you already know:

main()
{
    size_t arr_size = 2000;
    char *p=NULL;
    p=malloc(arr_size * sizeof(char));
    printf("size of p = %d\n",arr_size);
}

Edit - If the malloc fails to allocate the size you wanted, it won't give you a pointer to a smaller buffer, but it will return NULL.