Is it safe to delete a NULL pointer

Question

Is it safe to delete a NULL pointer   And is it a good coding style

User · Answer

I have experienced that it is not safe  VS2010  to delete   NULL  i e  array syntax   I m not sure whether this is according to the C   standard   It is safe to delete NULL  scalar syntax

User · Answer

From the C  0x draft Standard       5 3 5 2 -       In either   alternative  the value of the operand   of delete may be a null pointer   value          Of course  no one would ever do  delete  of a pointer with NULL value  but it is safe to do  Ideally one should not have code that does deletion of a NULL pointer  But it is sometimes useful when deletion of pointers  e g  in a container  happens in a loop  Since delete of a NULL pointer value is safe  one can really write the deletion logic without explicit checks for NULL operand to delete   As an aside  C Standard  7 20 3 2 also says that  free  on a NULL pointer does no action      The free function causes the space   pointed to by ptr to be deallocated    that is  made available for further   allocation  If ptr is a null pointer    no action occurs

User · Answer

To complement ruslik s answer  in C  14 you can use this construction   delete std  exchange heapObject  nullptr

User · Answer

Deleting a null pointer has no effect   It s not good coding style necessarily because it s not needed  but it s not bad either   If you are searching for good coding practices consider using smart pointers instead so then you don t need to delete at all

User · Answer

Yes it is safe   There s no harm in deleting a null pointer  it often reduces the number of tests at the tail of a function if the unallocated pointers are initialized to zero and then simply deleted     Since the previous sentence has caused confusion  an example     which isn t exception safe     of what is being described   void somefunc void        SomeType  pst   0      AnotherType  pat   0               pst   new SomeType              if                     pat   new AnotherType 10                         if                        code using pat sometimes               delete   pat      delete pst      There are all sorts of nits that can be picked with the sample code  but the concept is  I hope  clear   The pointer variables are initialized to zero so that the delete operations at the end of the function do not need to test whether they re non-null in the source code  the library code performs that check anyway

User · Answer

It is safe unless you overloaded the delete operator  if you overloaded the delete operator and not handling null condition then it is not safe at all

User · Answer

delete performs the check anyway  so checking it on your side adds overhead and looks uglier  A very good practice is setting the pointer to NULL after delete  helps avoiding double deletion and other similar memory corruption problems    I d also love if delete by default was setting the parameter to NULL like in    define my delete x   delete x  x   NULL      I know about R and L values  but wouldn t it be nice

[c++] Is it safe to delete a NULL pointer?

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