What REALLY happens when you don’t free after malloc before program termination?

by

Just about every modern operating system will recover all the allocated memory space after a program exits. The only exception I can think of might be something like Palm OS where the program’s static storage and runtime memory are pretty much the same thing, so not freeing might cause the program to take up more storage. (I’m only speculating here.)

So generally, there’s no harm in it, except the runtime cost of having more storage than you need. Certainly in the example you give, you want to keep the memory for a variable that might be used until it’s cleared.

However, it’s considered good style to free memory as soon as you don’t need it any more, and to free anything you still have around on program exit. It’s more of an exercise in knowing what memory you’re using, and thinking about whether you still need it. If you don’t keep track, you might have memory leaks.

On the other hand, the similar admonition to close your files on exit has a much more concrete result – if you don’t, the data you wrote to them might not get flushed, or if they’re a temp file, they might not get deleted when you’re done. Also, database handles should have their transactions committed and then closed when you’re done with them. Similarly, if you’re using an object oriented language like C++ or Objective C, not freeing an object when you’re done with it will mean the destructor will never get called, and any resources the class is responsible might not get cleaned up.

More Related Contents:

  1. How do free and malloc work in C?
  2. Setting variable to NULL after free
  3. Should I free memory before exit?
  4. free char*: invalid next size (fast) [duplicate]
  5. C – Accessing data AFTER memory has been free()ed?
  6. malloc implementation?
  7. If free() knows the length of my array, why can’t I ask for it in my own code?
  8. Why do I get different results when I dereference a pointer after freeing it?
  9. C: Correctly freeing memory of a multi-dimensional array
  10. Is freeing allocated memory needed when exiting a program in C
  11. Problem usage memory in C
  12. Why exactly should I not call free() on variables not allocated by malloc()?
  13. How are we able to access the pointer after deallocating the memory?
  14. Code for malloc and free
  15. How do I correctly set up, access, and free a multidimensional array in C?
  16. Why malloc+memset is slower than calloc?
  17. C Programming: malloc() inside another function
  18. Create a wrapper function for malloc and free in C
  19. Writing to pointer out of bounds after malloc() not causing error
  20. C – allocating a matrix in a function
  21. Incompatible implicit declaration of built-in function ‘malloc’
  22. Should one really set pointers to `NULL` after freeing them?
  23. Why do we cast return value of malloc? [duplicate]
  24. Explain this implementation of malloc from the K&R book
  25. Find malloc() array length in C? [duplicate]
  26. How to determine the size of an allocated C buffer? [duplicate]
  27. C – freeing structs
  28. Malloc function (dynamic memory allocation) resulting in an error when it is used globally
  29. Is typecast required in malloc? [duplicate]
  30. Where do malloc() and free() store allocated sizes and addresses?

Leave a Comment