Deleting an object in C

Question

Here is a sample code that I have   void test        Object1  obj   new Object1                      delete obj      I run it in Visual Studio  and it crashes at the line with  delete obj    Isn t this the normal way to free the memory associated with an object  I realized that it automatically invokes the destructor    is this normal     Here is a code snippet       if node- gt isleaf                  vector lt string gt  vec   node- gt L          vec push back node- gt code           sort vec begin    vec end              Mesh  msh   loadLeaves vec  node- gt code            Simplification smp msh            smp simplifyErrorBased errorThreshold            int meshFaceCount   msh- gt faces size             saveLeaves vec  msh            delete msh          loadleaves   is a function that reads a mesh from disk and creates a Mesh object and returns it  think of vec and node- gt code are just information about the file to be opened   Should I remove the delete msh  line

User · Answer

if it crashes on the delete line then you have almost certainly somehow corrupted the heap  We would need to see more code to diagnose the problem since the example you presented has no errors   Perhaps you have a buffer overflow on the heap which corrupted the heap structures or even something as simple as a  double free   or in the c   case  double delete     Also  as The Fuzz noted  you may have an error in your destructor as well   And yes  it is completely normal and expected for delete to invoke the destructor  that is in fact one of its two purposes  call destructor then free memory

User · Answer

Isn t this the normal way to free the memory associated with an object    This is a common way of managing dynamically allocated memory  but it s not a good way to do so   This sort of code is brittle because it is not exception-safe   if an exception is thrown between when you create the object and when you delete it  you will leak that object   It is far better to use a smart pointer container  which you can use to get scope-bound resource management  it s more commonly called resource acquisition is initialization  or RAII      As an example of automatic resource management   void test         std  auto ptr lt Object1 gt  obj1 new Object1         The object is automatically deleted when the scope ends    Depending on your use case  auto ptr might not provide the semantics you need   In that case  you can consider using shared ptr   As for why your program crashes when you delete the object  you have not given sufficient code for anyone to be able to answer that question with any certainty

User · Answer

Your code is indeed using the normal way to create and delete a dynamic object   Yes  it s perfectly normal  and indeed guaranteed by the language standard   that delete will call the object s destructor  just like new has to invoke the constructor   If you weren t instantiating Object1 directly but some subclass thereof  I d remind you that any class intended to be inherited from must have a virtual destructor  so that the correct subclass s destructor can be invoked in cases analogous to this one  -- but if your sample code is indeed representative of your actual code  this cannot be your current problem -- must be something else  maybe in the destructor code you re not showing us  or some heap-corruption in the code you re not showing within that function or the ones it calls      BTW  if you re always going to delete the object just before you exit the function which instantiates it  there s no point in making that object dynamic -- just declare it as a local  storage class auto  as is the default  variable of said function

User · Answer

saveLeaves vec msh   I m assuming takes the msh pointer and puts it inside of vec  Since msh is just a pointer to the memory  if you delete it  it will also get deleted inside of the vector

User · Answer

Isn t this the normal way to free the memory associated with an object    Yes  it is      I realized that it automatically invokes the destructor    is this normal    Yes  Make sure that you did not double delete your object

User · Answer

Just an update of James  answer   Isn t this the normal way to free the memory associated with an object   Yes  It is the normal way to free memory  But new delete operator always leads to memory leak problem  Since c  17 already removed auto ptr auto ptr  I suggest shared ptr or unique ptr to handle the memory problems  void test         std  shared ptr lt Object1 gt  obj1 new Object1         The object is automatically deleted when the scope ends or reference counting reduces to 0    The reason for removing auto ptr is that auto ptr is not stable in case of coping semantics If you are sure about no coping happening during the scope  a unique ptr is suggested  If there is a circular reference between the pointers  I suggest having a look at weak ptr

[c++] Deleting an object in C++

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