error use of deleted function

Question

I ve been working on some C   code that a friend has written and I get the following error that I have never seen before when compiling with gcc4 6   error  use of deleted function     GameFSM  lt std  array lt C  2ul gt   gt   hdealt  hdealt      is implicitly deleted because the default definition would be ill-formed  uninitialized non-static const member    const h t FlopPokerGameFSM  lt std  array lt C  2ul gt   gt   hdealt  h      Edit  This comes from a part of the code using boost MSM  Boost Webpage  Edit2  There is no   delete   used anywhere in the sourcecode   Generally speaking  what does this error mean  What should I be looking for when this type of error occurs

User · Answer

I encountered this error when inheriting from an abstract class and not implementing all of the pure virtual methods in my subclass

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The error message clearly says that the default constructor has been deleted implicitly  It even says why  the class contains a non-static  const variable  which would not be initialized by the default ctor   class X       const int x       Since X  x is const  it must be initialized -- but a default ctor wouldn t normally initialize it  because it s a POD type   Therefore  to get a default ctor  you need to define one yourself  and it must initialize x   You can get the same kind of situation with a member that s a reference   class X        whatever  amp x       It s probably worth noting that both of these will also disable implicit creation of an assignment operator as well  for essentially the same reason  The implicit assignment operator normally does members-wise assignment  but with a const member or reference member  it can t do that because the member can t be assigned  To make assignment work  you need to write your own assignment operator   This is why a const member should typically be static -- when you do an assignment  you can t assign the const member anyway  In a typical case all your instances are going to have the same value so they might as well share access to a single variable instead of having lots of copies of a variable that will all have the same value   It is possible  of course  to create instances with different values though -- you  for example  pass a value when you create the object  so two different objects can have two different values  If  however  you try to do something like swapping them  the const member will retain its original value instead of being swapped

User · Answer

gcc 4 6 supports a new feature of deleted functions  where you can write  hdealt     delete    to disable the default constructor   Here the compiler has obviously seen that a default constructor can not be generated  and  delete d it for you

User · Answer

You are using a function  which is marked as deleted  Eg   int doSomething  int     delete    The  delete is a new feature of C  0x  It means the compiler should immediately stop compiling and complain  this function is deleted  once the user use such function   If you see this error  you should check the function declaration for  delete    To know more about this new feature introduced in C  0x  check this out

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Switching from gcc 4 6 to gcc 4 8 resolved this for me

User · Answer

In the current C  0x standard you can explicitly disable default constructors with the delete syntax  e g   MyClass     delete    Gcc 4 6 is the first version to support this syntax  so maybe that is the problem

[c++] error: use of deleted function

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