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
Read from and write to dynamic memory:
// 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]);
Try it Yourself »
ptr[3] prints 0, because calloc() writes zeroes into all of the memory it allocates.
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]);
Try it Yourself »
On most computers, the four bytes of the number 1684234849 are the character codes for a, b, c and d. That is why the same memory can be read as one int, or as four char values.
