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Select struct definition from multiple ones based on platform



The Next CEO of Stack OverflowPartial class definition on C++?How can friend function be declared for only one particular function and class?Mutual class instances in C++Platform Independence with C++. Detection and CompilationBool sorted insert function with check if int already exist in listWhy does microsoft use so many macros in their C++ code?C++: Cross reference in subclassesNot default destructor causes incomplete type errorWhy am I getting multiple definition error when header included?#ifdef [true condition] #endif block. Commenting out #ifdef & #endif lines changes compile?










2















Is it possible to have one struct, but two definitions, where the definition is selected via a #define macro? For example:



platform.h



struct Context;


platform_win32.cc:



#include "platform.h"

struct Context

// win32 specific implementation..
bool win;



platform_linux.cc:



#include "platform.h"

struct Context

//Linux specific implementation..
bool lin;



platform.cc:



#define WIN32 //For testing reasons

#ifdef WIN32
#include "platform_win32.cc"
#endif

#ifdef LINUX
#include "platform_linux.cc"
#endif


main.cc:



#include "platform.h"

int main()

Context *context = new Context;
context->win=true;

return 0;



But, this does not compile and returns:



error: invalid use of incomplete type 'struct Context'
note: forward declaration of 'struct Context'


How do I fix this?










share|improve this question




























    2















    Is it possible to have one struct, but two definitions, where the definition is selected via a #define macro? For example:



    platform.h



    struct Context;


    platform_win32.cc:



    #include "platform.h"

    struct Context

    // win32 specific implementation..
    bool win;



    platform_linux.cc:



    #include "platform.h"

    struct Context

    //Linux specific implementation..
    bool lin;



    platform.cc:



    #define WIN32 //For testing reasons

    #ifdef WIN32
    #include "platform_win32.cc"
    #endif

    #ifdef LINUX
    #include "platform_linux.cc"
    #endif


    main.cc:



    #include "platform.h"

    int main()

    Context *context = new Context;
    context->win=true;

    return 0;



    But, this does not compile and returns:



    error: invalid use of incomplete type 'struct Context'
    note: forward declaration of 'struct Context'


    How do I fix this?










    share|improve this question


























      2












      2








      2








      Is it possible to have one struct, but two definitions, where the definition is selected via a #define macro? For example:



      platform.h



      struct Context;


      platform_win32.cc:



      #include "platform.h"

      struct Context

      // win32 specific implementation..
      bool win;



      platform_linux.cc:



      #include "platform.h"

      struct Context

      //Linux specific implementation..
      bool lin;



      platform.cc:



      #define WIN32 //For testing reasons

      #ifdef WIN32
      #include "platform_win32.cc"
      #endif

      #ifdef LINUX
      #include "platform_linux.cc"
      #endif


      main.cc:



      #include "platform.h"

      int main()

      Context *context = new Context;
      context->win=true;

      return 0;



      But, this does not compile and returns:



      error: invalid use of incomplete type 'struct Context'
      note: forward declaration of 'struct Context'


      How do I fix this?










      share|improve this question
















      Is it possible to have one struct, but two definitions, where the definition is selected via a #define macro? For example:



      platform.h



      struct Context;


      platform_win32.cc:



      #include "platform.h"

      struct Context

      // win32 specific implementation..
      bool win;



      platform_linux.cc:



      #include "platform.h"

      struct Context

      //Linux specific implementation..
      bool lin;



      platform.cc:



      #define WIN32 //For testing reasons

      #ifdef WIN32
      #include "platform_win32.cc"
      #endif

      #ifdef LINUX
      #include "platform_linux.cc"
      #endif


      main.cc:



      #include "platform.h"

      int main()

      Context *context = new Context;
      context->win=true;

      return 0;



      But, this does not compile and returns:



      error: invalid use of incomplete type 'struct Context'
      note: forward declaration of 'struct Context'


      How do I fix this?







      c++ api cross-platform






      share|improve this question















      share|improve this question













      share|improve this question




      share|improve this question








      edited Mar 8 at 13:06







      Cryonic

















      asked Mar 8 at 12:48









      CryonicCryonic

      135




      135






















          2 Answers
          2






          active

          oldest

          votes


















          0














          Firstly, the declare of type should be write into '.h' file, other than '.cc' or '.c' file.



          Secondly, you can declare different type of struct for different platform by #define, like you did.



          For example:



          platform_win32.h:



          struct Context

          // win32 specific implementation..
          bool field1;
          bool field2;
          bool field_win_specified;



          platform_linux.h:



          struct Context

          //Linux specific implementation..
          bool field1;
          bool field2;
          bool field_linux_specified;



          platform.h:



          #ifdef WIN32
          #include "platform_win32.h"
          #endif

          #ifdef LINUX
          #include "platform_linux.h"
          #endif


          main.cc:



          #include "platform.h"

          int main()

          Context *context = new Context;
          context->field1=true;

          return 0;






          share|improve this answer























          • Bye the way, because we can not avoid to include a '.h' file more than one time, you should to define tokens to clear up these compiling error(s): e.g., in platform_linux.h file: ``` #ifndef PLATFORM_LINUX_H_ #define PLATFORM_LINUX_H_ //...... #endif // PLATFORM_LINUX_H__ ```

            – Yuanhui
            Mar 8 at 13:37



















          0














          For forward-declare like struct Context;



          The main rule is that you can only use where memory layout (and thus member functions and data members) do not need to be known in the file you forward-declare it.



          Possible fix:



          platform.h



          #define WIN32 //For testing reasons

          #ifdef WIN32
          #include "platform_win32.h"
          #endif

          #ifdef LINUX
          #include "platform_linux.h"
          #endif


          platform_win32.h



          struct Context

          // win32 specific implementation..
          bool win;



          platform_linux.h



          struct Context

          //Linux specific implementation..
          bool lin;



          main.cc



          #include "platform.h"

          int main()

          Context *context = new Context;
          context->win=true;

          return 0;






          share|improve this answer























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            2 Answers
            2






            active

            oldest

            votes








            2 Answers
            2






            active

            oldest

            votes









            active

            oldest

            votes






            active

            oldest

            votes









            0














            Firstly, the declare of type should be write into '.h' file, other than '.cc' or '.c' file.



            Secondly, you can declare different type of struct for different platform by #define, like you did.



            For example:



            platform_win32.h:



            struct Context

            // win32 specific implementation..
            bool field1;
            bool field2;
            bool field_win_specified;



            platform_linux.h:



            struct Context

            //Linux specific implementation..
            bool field1;
            bool field2;
            bool field_linux_specified;



            platform.h:



            #ifdef WIN32
            #include "platform_win32.h"
            #endif

            #ifdef LINUX
            #include "platform_linux.h"
            #endif


            main.cc:



            #include "platform.h"

            int main()

            Context *context = new Context;
            context->field1=true;

            return 0;






            share|improve this answer























            • Bye the way, because we can not avoid to include a '.h' file more than one time, you should to define tokens to clear up these compiling error(s): e.g., in platform_linux.h file: ``` #ifndef PLATFORM_LINUX_H_ #define PLATFORM_LINUX_H_ //...... #endif // PLATFORM_LINUX_H__ ```

              – Yuanhui
              Mar 8 at 13:37
















            0














            Firstly, the declare of type should be write into '.h' file, other than '.cc' or '.c' file.



            Secondly, you can declare different type of struct for different platform by #define, like you did.



            For example:



            platform_win32.h:



            struct Context

            // win32 specific implementation..
            bool field1;
            bool field2;
            bool field_win_specified;



            platform_linux.h:



            struct Context

            //Linux specific implementation..
            bool field1;
            bool field2;
            bool field_linux_specified;



            platform.h:



            #ifdef WIN32
            #include "platform_win32.h"
            #endif

            #ifdef LINUX
            #include "platform_linux.h"
            #endif


            main.cc:



            #include "platform.h"

            int main()

            Context *context = new Context;
            context->field1=true;

            return 0;






            share|improve this answer























            • Bye the way, because we can not avoid to include a '.h' file more than one time, you should to define tokens to clear up these compiling error(s): e.g., in platform_linux.h file: ``` #ifndef PLATFORM_LINUX_H_ #define PLATFORM_LINUX_H_ //...... #endif // PLATFORM_LINUX_H__ ```

              – Yuanhui
              Mar 8 at 13:37














            0












            0








            0







            Firstly, the declare of type should be write into '.h' file, other than '.cc' or '.c' file.



            Secondly, you can declare different type of struct for different platform by #define, like you did.



            For example:



            platform_win32.h:



            struct Context

            // win32 specific implementation..
            bool field1;
            bool field2;
            bool field_win_specified;



            platform_linux.h:



            struct Context

            //Linux specific implementation..
            bool field1;
            bool field2;
            bool field_linux_specified;



            platform.h:



            #ifdef WIN32
            #include "platform_win32.h"
            #endif

            #ifdef LINUX
            #include "platform_linux.h"
            #endif


            main.cc:



            #include "platform.h"

            int main()

            Context *context = new Context;
            context->field1=true;

            return 0;






            share|improve this answer













            Firstly, the declare of type should be write into '.h' file, other than '.cc' or '.c' file.



            Secondly, you can declare different type of struct for different platform by #define, like you did.



            For example:



            platform_win32.h:



            struct Context

            // win32 specific implementation..
            bool field1;
            bool field2;
            bool field_win_specified;



            platform_linux.h:



            struct Context

            //Linux specific implementation..
            bool field1;
            bool field2;
            bool field_linux_specified;



            platform.h:



            #ifdef WIN32
            #include "platform_win32.h"
            #endif

            #ifdef LINUX
            #include "platform_linux.h"
            #endif


            main.cc:



            #include "platform.h"

            int main()

            Context *context = new Context;
            context->field1=true;

            return 0;







            share|improve this answer












            share|improve this answer



            share|improve this answer










            answered Mar 8 at 13:10









            YuanhuiYuanhui

            307212




            307212












            • Bye the way, because we can not avoid to include a '.h' file more than one time, you should to define tokens to clear up these compiling error(s): e.g., in platform_linux.h file: ``` #ifndef PLATFORM_LINUX_H_ #define PLATFORM_LINUX_H_ //...... #endif // PLATFORM_LINUX_H__ ```

              – Yuanhui
              Mar 8 at 13:37


















            • Bye the way, because we can not avoid to include a '.h' file more than one time, you should to define tokens to clear up these compiling error(s): e.g., in platform_linux.h file: ``` #ifndef PLATFORM_LINUX_H_ #define PLATFORM_LINUX_H_ //...... #endif // PLATFORM_LINUX_H__ ```

              – Yuanhui
              Mar 8 at 13:37

















            Bye the way, because we can not avoid to include a '.h' file more than one time, you should to define tokens to clear up these compiling error(s): e.g., in platform_linux.h file: ``` #ifndef PLATFORM_LINUX_H_ #define PLATFORM_LINUX_H_ //...... #endif // PLATFORM_LINUX_H__ ```

            – Yuanhui
            Mar 8 at 13:37






            Bye the way, because we can not avoid to include a '.h' file more than one time, you should to define tokens to clear up these compiling error(s): e.g., in platform_linux.h file: ``` #ifndef PLATFORM_LINUX_H_ #define PLATFORM_LINUX_H_ //...... #endif // PLATFORM_LINUX_H__ ```

            – Yuanhui
            Mar 8 at 13:37














            0














            For forward-declare like struct Context;



            The main rule is that you can only use where memory layout (and thus member functions and data members) do not need to be known in the file you forward-declare it.



            Possible fix:



            platform.h



            #define WIN32 //For testing reasons

            #ifdef WIN32
            #include "platform_win32.h"
            #endif

            #ifdef LINUX
            #include "platform_linux.h"
            #endif


            platform_win32.h



            struct Context

            // win32 specific implementation..
            bool win;



            platform_linux.h



            struct Context

            //Linux specific implementation..
            bool lin;



            main.cc



            #include "platform.h"

            int main()

            Context *context = new Context;
            context->win=true;

            return 0;






            share|improve this answer



























              0














              For forward-declare like struct Context;



              The main rule is that you can only use where memory layout (and thus member functions and data members) do not need to be known in the file you forward-declare it.



              Possible fix:



              platform.h



              #define WIN32 //For testing reasons

              #ifdef WIN32
              #include "platform_win32.h"
              #endif

              #ifdef LINUX
              #include "platform_linux.h"
              #endif


              platform_win32.h



              struct Context

              // win32 specific implementation..
              bool win;



              platform_linux.h



              struct Context

              //Linux specific implementation..
              bool lin;



              main.cc



              #include "platform.h"

              int main()

              Context *context = new Context;
              context->win=true;

              return 0;






              share|improve this answer

























                0












                0








                0







                For forward-declare like struct Context;



                The main rule is that you can only use where memory layout (and thus member functions and data members) do not need to be known in the file you forward-declare it.



                Possible fix:



                platform.h



                #define WIN32 //For testing reasons

                #ifdef WIN32
                #include "platform_win32.h"
                #endif

                #ifdef LINUX
                #include "platform_linux.h"
                #endif


                platform_win32.h



                struct Context

                // win32 specific implementation..
                bool win;



                platform_linux.h



                struct Context

                //Linux specific implementation..
                bool lin;



                main.cc



                #include "platform.h"

                int main()

                Context *context = new Context;
                context->win=true;

                return 0;






                share|improve this answer













                For forward-declare like struct Context;



                The main rule is that you can only use where memory layout (and thus member functions and data members) do not need to be known in the file you forward-declare it.



                Possible fix:



                platform.h



                #define WIN32 //For testing reasons

                #ifdef WIN32
                #include "platform_win32.h"
                #endif

                #ifdef LINUX
                #include "platform_linux.h"
                #endif


                platform_win32.h



                struct Context

                // win32 specific implementation..
                bool win;



                platform_linux.h



                struct Context

                //Linux specific implementation..
                bool lin;



                main.cc



                #include "platform.h"

                int main()

                Context *context = new Context;
                context->win=true;

                return 0;







                share|improve this answer












                share|improve this answer



                share|improve this answer










                answered Mar 8 at 13:11









                C_RajC_Raj

                1194




                1194



























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