Meaning of delete after function declaration

Question

class my class               my class my class const  amp     delete               What does   delete mean in that context   Are there any other  modifiers   other than   0 and   delete

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This excerpt from The C   Programming Language  4th Edition  - Bjarne Stroustrup book talks about the real purpose behind using  delete      3 3 4 Suppressing Operations      Using the default copy or move for a class in a hierarchy is typically   a disaster  given only a pointer to a base  we simply don   t know what   members the derived class has  so we can   t know how to copy   them  So  the best thing to do is usually to delete the default copy   and move operations  that is  to eliminate the default definitions of   those two operations   class Shape   public    Shape const Shape amp    delete     no copy operations   Shape amp  operator  const Shape amp    delete     Shape Shape amp  amp    delete     no move operations   Shape amp  operator  Shape amp  amp    delete      Shape                        Now an attempt to copy a Shape will be caught by the compiler       The  delete mechanism is general  that is  it can be used to suppress any operation

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Deleting a function is a C  11 feature      The common idiom of  prohibiting copying  can now be expressed   directly   class X                  X amp  operator  const X amp     delete      Disallow copying     X const X amp     delete                      The  delete  mechanism can be used for any function  For example  we   can eliminate an undesired conversion like this   struct Z                   Z long long          can initialize with an long long              Z long    delete     but not anything less

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A deleted function is implicitly inline   Addendum to existing answers       And a deleted function shall be the first declaration of the function  except for deleting explicit specializations of function templates - deletion should be at the first declaration of the specialization   meaning you cannot declare a function and later delete it  say  at its definition local to a translation unit   Citing  dcl fct def delete  4      A deleted function is implicitly inline    Note  The one-definition   rule     basic def odr     applies to deleted definitions       end note   A deleted definition   of a function shall be the first declaration of the function or  for   an explicit specialization of a function template  the first   declaration of that specialization    Example   struct sometype     sometype       sometype  sometype     delete          ill-formed  not first declaration           end example     A primary function template with a deleted definition can be specialized  Albeit a general rule of thumb is to avoid specializing function templates as specializations do not participate in the first step of overload resolution  there are arguable some contexts where it can be useful  E g  when using a non-overloaded primary function template with no definition to match all types which one would not like implicitly converted to an otherwise matching-by-conversion overload  i e   to implicitly remove a number of implicit-conversion matches by only implementing exact type matches in the explicit specialization of the non-defined  non-overloaded primary function template   Before the deleted function concept of C  11  one could do this by simply omitting the definition of the primary function template  but this gave obscure undefined reference errors that arguably gave no semantic intent whatsoever from the author of primary function template  intentionally omitted    If we instead explicitly delete the primary function template  the error messages in case no suitable explicit specialization is found becomes much nicer  and also shows that the omission deletion of the primary function template s definition was intentional    include  lt iostream gt   include  lt string gt   template lt  typename T  gt  void use only explicit specializations T t    template lt  gt  void use only explicit specializations lt int gt  int t        std  cout  lt  lt   int     lt  lt  t     int main         const int num   42      const std  string str    foo       use only explicit specializations num       int  42       use only explicit specializations str      undefined reference to  void use only explicit specializations lt          However  instead of simply omitting a definition for the primary function template above  yielding an obscure undefined reference error when no explicit specialization matches  the primary template definition can be deleted    include  lt iostream gt   include  lt string gt   template lt  typename T  gt  void use only explicit specializations T t    delete   template lt  gt  void use only explicit specializations lt int gt  int t        std  cout  lt  lt   int     lt  lt  t     int main         const int num   42      const std  string str    foo       use only explicit specializations num       int  42     use only explicit specializations str          error  call to deleted function  use only explicit specializations          note  candidate function  with T   std    1  basic string lt char gt   has         been explicitly deleted        void use only explicit specializations T t    delete         Yielding a more more readable error message  where the deletion intent is also clearly visible  where an undefined reference error could lead to the developer thinking this an unthoughtful mistake    Returning to why would we ever want to use this technique  Again  explicit specializations could be useful to implicitly remove implicit conversions    include  lt cstdint gt   include  lt iostream gt   void warning at best int8 t num         std  cout  lt  lt   I better use -Werror and -pedantic       lt  lt   num  lt  lt    n      template lt  typename T  gt  void only for signed T t    delete   template lt  gt  void only for signed lt int8 t gt  int8 t t        std  cout  lt  lt   UB safe  1 byte     lt  lt   t  lt  lt    n      template lt  gt  void only for signed lt int16 t gt  int16 t t        std  cout  lt  lt   UB safe  2 bytes     lt  lt   t  lt  lt    n      int main         const int8 t a   42      const uint8 t b   255U      const int16 t c   255      const float d   200 F       warning at best a      42     warning at best b      implementation-defined behaviour  no diagnostic required     warning at best c      narrowing  -Wconstant-conversion warning     warning at best d      undefined behaviour       only for signed a       only for signed c          only for signed b            error  call to deleted function  only for signed          note  candidate function  with T   unsigned char                has been explicitly deleted        void only for signed T t    delete            only for signed d          error  call to deleted function  only for signed          note  candidate function  with T   float                has been explicitly deleted        void only for signed T t    delete

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Are there any other  modifiers   other than   0 and   delete     Since it appears no one else answered this question  I should mention that there is also  default   https   docs microsoft com en-us cpp cpp explicitly-defaulted-and-deleted-functions explicitly-defaulted-functions

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0 means that a function is pure virtual and you cannot instantiate an object from this class  You need to derive from it and implement this method   delete means that the compiler will not generate those constructors for you  AFAIK this is only allowed on copy constructor and assignment operator  But I am not too good at the upcoming standard

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New C  0x standard  Please see section 8 4 3 in the N3242 working draft

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This is new thing in C   0x standards where you can delete an inherited function

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The coding standards I ve worked with have had the following for most of class declarations       coding standard  disallow when not used T void                     delete     default ctor     1   T void                    delete     default dtor     2  T const T amp                  delete     copy ctor        3  T const T amp  amp                 delete     move ctor        4  T amp  operator   const T amp      delete     copy assignment  5  T amp  operator   const T amp  amp     delete     move assignment  6    If you use any of these 6  you simply comment out the corresponding line     Example  class FizzBus require only dtor  and thus do not use the other 5       coding standard  disallow when not used FizzBuzz void                            delete     default ctor  1      FizzBuzz void                                   dtor          2  FizzBuzz const FizzBuzz amp                  delete     copy ctor     3  FizzBuzz amp  operator   const FizzBuzz amp      delete     copy assig    4  FizzBuzz const FizzBuzz amp  amp                 delete     move ctor     5  FizzBuzz amp  operator   const FizzBuzz amp  amp     delete     move assign   6    We comment out only 1 here  and install the implementation of it else where  probably where the coding standard suggests    The other 5  of 6  are disallowed with delete     You can also use    delete  to disallow implicit promotions of different sized values     example     disallow implicit promotions  template  lt class T gt  operator T void                 delete  template  lt class T gt  Vuint64 amp  operator    const T    delete  template  lt class T gt  Vuint64 amp  operator    const T    delete  template  lt class T gt  Vuint64 amp  operator amp    const T    delete

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delete is a feature introduce in C  11  As per  delete it will not allowed to call that function   In detail   Suppose in a class   Class ABC   Int d   Public    ABC amp  operator   const ABC amp  obj   delete               While calling this function for obj assignment it will not allowed  Means assignment operator is going to restrict to copy from one object to another

[c++] Meaning of = delete after function declaration

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