Using C base class constructors

Question

While working with templates I ran into a need to make a base class constructors accessible from inherited classes for object creation to decrease copy paste operations  I was thinking to do this through using keyword in same manner with functions case  but that not work   class A   public       A int val         class B   public A       class C   public A   public      C const string  amp val         class D   public A   public      D const string  amp val         using A  A                  g   error  A  A names constructor     void main         B b 10                     Ok     A  A constructor is not overlapped      C c 10                     error  no matching function to call to  C  C int       So my question  Is there any way to import a base class constructors after new ones in inherited class been declared   Or there is only one alternative to declare new constructors and call a base ones from initializer list

User · Answer

No  that s not how it is done  Normal way to initialize the base class is in the initialization list      class A   public       A int val         class B   public A   public    B  int v    A  v                void main         B b 10

User · Answer

Prefer initialization   class C   public A   public      C const string  amp val    A anInt          In C  11  you can use inheriting constructors  which has the syntax seen in your example D     Update  Inheriting Constructors have been available in GCC since version 4 8     If you don t find initialization appealing  e g  due to the number of possibilities in your actual case   then you might favor this approach for some TMP constructs   class A   public       A          virtual  A          void init int    std  cout  lt  lt   A n         class B   public A   public      B     A          void init int    std  cout  lt  lt   B n         class C   public A   public      C     A          void init int    std  cout  lt  lt   C n         class D   public A   public      D     A          using A  init      void init const std  string amp  s    std  cout  lt  lt   D - gt     lt  lt  s  lt  lt    n         int main         B b  b init 10       C c  c init 10       D d  d init 10   d init  a         return 0

User · Answer

Here is a good discussion about superclass constructor calling rules  You always want the base class constructor to be called before the derived class constructor in order to form an object properly  Which is why this form is used    B  int v    A  v

User · Answer

Yes  Since C  11   struct B2       B2 int   13  int   42      struct D2   B2       using B2  B2     The set of inherited constructors is    1  B2 const B2 amp      2  B2 B2 amp  amp      3  B2 int   13  int   42     4  B2 int   13     5  B2       D2 has the following constructors     1  D2      2  D2 const D2 amp      3  D2 D2 amp  amp      4  D2 int  int   lt - inherited    5  D2 int   lt - inherited      For additional information see http   en cppreference com w cpp language using declaration

User · Answer

You ll need to declare constructors in each of the derived classes  and then call the base class constructor from the initializer list   class D   public A   public      D const string  amp val    A 0         D  int val     A  val          D variable1   Hello     D variable2  10      C  11 allows you to use the using A  A syntax you use in your decleration of D  but C  11 features aren t supported by all compilers just now  so best to stick with the older C   methods until this feature is implemented in all the compilers your code will be used with

[c++] Using C++ base class constructors?

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