dynamic allocation/deallocation of 2D & 3D arrays

by

You can also allocate one array and compute individual indices. This requires fewer allocator calls and results in both less fragmentation and better cache use.

typedef struct {
  int a;
  int b;
  int* data;
} Int2d;

Int2d arr2d = { 2, 3 };
arr2d.data = malloc(arr2d.a * arr2d.b * sizeof *arr2d.data);

Now arr2d[r][c] becomes arr2d.data[r * arr2d.b + c]. Deallocation is a single free() away. As a bonus you’re sure to always keep your dynamic array sizes with you.

Extrapolating to 3d:

typedef struct {
  int a;
  int b;
  int c;
  int* data;
} Int3d;

Int3d arr3d = { 2, 3, 4 };
arr3d.data = malloc(arr3d.a * arr3d.b * arr3d.c * sizeof *arr3d.data);

//arr3d[r][c][d]
// becomes:
arr3d.data[r * (arr3d.b * arr3d.c) + c * arr3d.c + d];

You should encapsulate these index operations (and the (de-)allocations for that matter) in a separate function or macro.

(The names for r, c, and d could be better—I was going for row, column, and depth. While a, b, and c are the limits of their corresponding dimensions, you might prefer something like n1, n2, n3 there, or even use an array for them.)

More Related Contents:

  1. Difference between static memory allocation and dynamic memory allocation
  2. Determine size of dynamically allocated memory in C
  3. Where in memory are my variables stored in C?
  4. Dynamic allocation of an unknown matrix in C
  5. How to dynamically allocate memory space for a string and get that string from user?
  6. Should I free char* initialized using string-literals?
  7. How can I create a dynamically sized array of structs?
  8. Using Dynamic Memory allocation for arrays
  9. Why would you ever want to allocate memory on the heap rather than the stack? [duplicate]
  10. Memory usage of current process in C
  11. dynamic allocating array of arrays in C
  12. Determining Stack Space with Visual Studio
  13. When should I use malloc in C and when don’t I?
  14. Force free() to return malloc memory back to OS
  15. Resizing an array with C
  16. C: pointer to array of pointers to structures (allocation/deallocation issues)
  17. Why exactly should I not call free() on variables not allocated by malloc()?
  18. Struct varies in memory size?
  19. What happens to memory after free()?
  20. whats the difference between dynamic memory allocation and normal memory allocation?
  21. When and why will a compiler initialise memory to 0xCD, 0xDD, etc. on malloc/free/new/delete?
  22. General guidelines to avoid memory leaks in C++ [closed]
  23. Function to dynamically allocate matrix
  24. Can I rely on malloc returning NULL?
  25. Is it good practice to free a NULL pointer in C? [duplicate]
  26. Why does “memset(arr, -1, sizeof(arr)/sizeof(int))” not clear an integer array to -1?
  27. malloc for struct and pointer in C
  28. What does “Memory allocated at compile time” really mean?
  29. How to avoid long chain of free’s (or deletes) after every error check in C?
  30. How to assign pointer address manually in C programming language?

Leave a Comment