C Access Memory

Access Dynamic Memory

Dynamic memory behaves like an array, with its data type specified by the type of the pointer.

As with arrays, to access an element in dynamic memory, refer to its index number:

ptr[0] = 12;

You can also dereference the pointer to access the first element:

*ptr = 12;

Example

  // Allocate memory
int *ptr;
ptr = calloc(4, sizeof(*ptr));

//
  Write to the memory
*ptr = 2;
ptr[1] = 4;
ptr[2] = 6;

// Read
  from the memory
printf("%d\n", *ptr);
printf("%d %d %d", ptr[1], ptr[2],
  ptr[3]);

A note about data types

Dynamic memory does not have its own data type, it is just a sequence of bytes. The data in the memory can be interpreted as a type based on the data type of the pointer.

In this example a pointer to four bytes can be interpreted as one int value (4 bytes) or as an array of 4 char values (1 byte each).

Example

  int *ptr1 = malloc(4);
char *ptr2 = (char*) ptr1;
ptr1[0] = 1684234849;
  printf("%d is %c %c %c %c", *ptr1, ptr2[0], ptr2[1], ptr2[2], ptr2[3]);