Class name does not name a type in C

Question

I just started programming in C    and I ve tried to create 2 classes where one will contain the other   File A h    ifndef  A h  define  A h  class A      public          A int id       private          int  id          B  b     HERE I GET A COMPILATION ERROR  B does not name a type      endif   File A cpp    include  A h   include  B h   include  lt cstdio gt   A  A int id    id id    b        printf  hello n the id is   d n    id       File B h    ifndef  B h  define  B h  class B      public          B        endif   File B cpp    include  B h   include  lt cstdio gt   B  B        printf  this is hello from B n        I first compile the B class and then the A class  but then I get the error message      A h 9  error     B    does not name a type   How do I fix this problem

User · Answer

NOTE  Because people searching with the same keyword will land on this page  I am adding this answer which is not the cause for this compiler error in the above mentioned case   I was facing this error when I had an enum declared in some file which had one of the elements having the same symbol as my class name   e g  if I declare an enum    A  B  C  in some file which is included in another file where I declare an object of class A   This was throwing the same compiler error message mentioning that Class A does not name a type  There was no circular dependency in my case   So  be careful while naming classes and declaring enums  which might be visible  imported and used externally in other files  in C

User · Answer

It actually happend to me because I mistakenly named the source file  quot something c quot  instead of  quot something cpp quot   I hope this helps someone  who has the same error

User · Answer

Include  B h  in  A h   That brings in the declaration of  B  for the compiler while compiling  A    The first bullet holds in the case of OP    3 4 1 7 -       A name used in the definition of a   class X outside of a member function   body or nested class definition27    shall be declared in one of the   following ways            before its use in   class X or be a member of a base class   of X  10 2   or           if X is a nested   class of class Y  9 7   before the   definition of X in Y  or shall be a   member of a base class of Y  this   lookup applies in turn to Y   s   enclosing classes  starting with the   innermost enclosing class  28  or           if   X is a local class  9 8  or is a   nested class of a local class  before   the definition of class X in a block   enclosing the definition of class X    or           if X is a member of namespace N    or is a nested class of a class that   is a member of N  or is a local class   or a nested class within a local class   of a function that is a member of N    before the definition of class X in   namespace N or in one of N   s enclosing   namespaces

User · Answer

when you define the class A  in A h  you explicitely say that the class has a member B   You MUST include  B h  in  A h

User · Answer

The preprocessor inserts the contents of the files A h and B h exactly where the include statement occurs  this is really just copy paste   When the compiler then parses A cpp  it finds the declaration of class A before it knows about class B  This causes the error you see  There are two ways to solve this    Include B h in A h  It is generally a good idea to include header files in the files where they are needed  If you rely on indirect inclusion though another header  or a special order of includes in the compilation unit  cpp-file   this will only confuse you and others as the project gets bigger  If you use member variable of type B in class A  the compiler needs to know the exact and complete declaration of B  because it needs to create the memory-layout for A  If  on the other hand  you were using a pointer or reference to B  then a forward declaration would suffice  because the memory the compiler needs to reserve for a pointer or reference is independent of the class definition  This would look like this   class B     forward declaration         class A   public      A int id   private      int  id      B  amp   b       This is very useful to avoid circular dependencies among headers    I hope this helps

User · Answer

Aren t you missing the  include  B h  in A h

User · Answer

You must first include B h from A h  B b  makes no sense until you have included B h

User · Answer

error  Class  does not name a type   Just in case someone does the same idiotic thing I did     I was creating a small test program from scratch and I typed Class instead of class  with a small C   I didn t take any notice of the quotes in the error message and spent a little too long not understanding my problem   My search for a solution brought me here so I guess the same could happen to someone else

User · Answer

The solution to my problem today was slightly different that the other answers here     In my case  the problem was caused by a missing close bracket     at the end of one of the header files in the include chain     Essentially  what was happening was that A was including B  Because B was missing a   somewhere in the file  the definitions in B were not correctly found in A    At first I thought I have circular dependency and added the forward declaration B  But then it started complaining about the fact that something in B was an incomplete type  That s how I thought of double checking the files for syntax errors

User · Answer

The problem is that you need to include B h in your A h file  The problem is that in the definition of A  the compiler still doesn t know what B is  You should include all the definitions of all the types you are using

[c++] Class name does not name a type in C++

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