C variable has initializer but incomplete type

Question

I am trying to compile 2 classes in C   with the following command   g   Cat cpp Cat main cpp -o Cat  But I receive the following error   Cat cpp 10 10  error  variable    Cat Joey    has initializer but incomplete type  Could someone explain to me what this means  What my files basically do is create a class  Cat cpp  and create an instance  Cat main cpp   Here is my source code   Cat cpp    include  lt iostream gt   include  lt string gt   class Cat   using namespace std   int main         Cat Joey  Joey        Joey Meow         return 0      Cat main cpp    include  lt iostream gt   include  lt string gt   using namespace std   class Cat       public          Cat string str          Variables         string name         Functions         void Meow        Cat  Cat string str        this- gt name   str     void Cat  Meow         cout  lt  lt   Meow    lt  lt  endl      return

User · Answer

You cannot define a variable of an incomplete type  You need to bring the whole definition of Cat into scope before you can create the local variable in main  I recommend that you move the definition of the type Cat to a header and include it from the translation unit that has main

User · Answer

It s not related to Ken s case directly  but such an error also can occur if you copied  h file and forgot to change  ifndef directive  In this case compiler will just skip definition of the class thinking that it s a duplication

User · Answer

Sometimes  the same error occurs when you forget to include the corresponding header

User · Answer

You use a forward declaration when you need a complete type   You must have a full definition of the class in order to use it   The usual way to go about this is   1  create a file Cat main h  2  move    include  lt string gt   class Cat       public          Cat std  string str          Variables         std  string name         Functions         void Meow         to Cat main h  Note that inside the header I removed using namespace std  and qualified string with std  string   3  include this file in both Cat main cpp and Cat cpp    include  Cat main h

User · Answer

I got a similar error and hit this page while searching the solution   With Qt this error can happen if you forget to add the QT WRAP CPP        step in your build to run meta object compiler  moc   Including the Qt header is not sufficient

[c++] C++ variable has initializer but incomplete type?

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