malloced array VS. variable-length-array [duplicate]

by

No they’re not absolutely the same. While both let you store the same number and type of objects, keep in mind that:

  • You can free() a malloced array, but you can’t free() a variable length array (although it goes out of scope and ceases to exist once the enclosing block is left). In technical jargon, they have different storage duration: allocated for malloc versus automatic for variable length arrays.
  • Although C has no concept of a stack, many implementation allocate a variable length array from the stack, while malloc allocates from the heap. This is an issue on stack-limited systems, e.g. many embedded operating systems, where the stack size is on the order of kB, while the heap is much larger.
  • It is also easier to test for a failed allocation with malloc than with a variable length array.
  • malloced memory can be changed in size with realloc(), while VLAs can’t (more precisely only by executing the block again with a different array dimension–which loses the previous contents).
  • A hosted C89 implementation only supports malloc().
  • A hosted C11 implementation may not support variable length arrays (it then must define __STDC_NO_VLA__ as the integer 1 according to C11 6.10.8.3).
  • Everything else I have missed 🙂

More Related Contents:

  1. Difference between array type and array allocated with malloc
  2. What’s the difference between a VLA and dynamic memory allocation via malloc?
  3. Why this program is crashing?
  4. How can I get the size of an array from a pointer in C?
  5. Why is it safer to use sizeof(*pointer) in malloc
  6. What’s the point of malloc(0)?
  7. Overriding ‘malloc’ using the LD_PRELOAD mechanism
  8. Using malloc for allocation of multi-dimensional arrays with different row lengths
  9. C compile error: “Variable-sized object may not be initialized”
  10. Why is malloc not “using up” the memory on my computer?
  11. newbie questions about malloc and sizeof
  12. Writing to pointer out of bounds after malloc() not causing error
  13. Maximum memory which malloc can allocate
  14. How does GCC implement variable-length arrays?
  15. free char*: invalid next size (fast) [duplicate]
  16. How to use realloc in a function in C
  17. Dynamically create an array of strings with malloc
  18. C Warning: Function returns address of local variable
  19. Do I really need malloc?
  20. malloc(sizeof(int)) vs malloc(sizeof(int *)) vs (int *)malloc(sizeof(int))
  21. malloc implementation?
  22. Using sizeof() on malloc’d memory [duplicate]
  23. Why do I get a warning every time I use malloc?
  24. An alternative for the deprecated __malloc_hook functionality of glibc
  25. Why does this intentionally incorrect use of strcpy not fail horribly?
  26. Is the operand of `sizeof` evaluated with a VLA?
  27. Is it required that a C Variable Length Array is allocated from the stack?
  28. Code for malloc and free
  29. checking that `malloc` succeeded in C
  30. Is typecast required in malloc? [duplicate]

Leave a Comment