How to use structs in class methods - return values and arguments

Projects Programming
1

Hi,

I am struggling to define structs and use them as return values and pass them as arguments to my class methods. I keep getting a string of errors:

TMGPS.cpp:6:1: error: 'UBX_MESSAGE_TYPE' does not name a type
UBX_MESSAGE_TYPE getPacketMessageType (UBX_MSG_CHECKSUM_HEADER pHeader, UBX_MESSAGE_TYPE msgTypes[]){

exit status 1
'UBX_MESSAGE_TYPE' does not name a type

Please if anyone could help? Below is a slimmed down version of my code. I am aware that my return data is pointless, but is just as an example.

tmGPS.h

 class tmGPS {
  
        private:
struct  UBX_MESSAGE_TYPE{
            unsigned char cls;
            unsigned char id;    
            unsigned short length;
            std::string mNemonic;
          } ;

struct UBX_MSG_CHECKSUM_HEADER {
            unsigned char cls;
            unsigned char id;
            unsigned short length;
          };

UBX_MESSAGE_TYPE getPacketMessageType(UBX_MSG_CHECKSUM_HEADER pHeader, UBX_MESSAGE_TYPE msgTypes[]);

public:
}

tmGPS.cpp

#include "tmGPS.h"

tmGPS::tmGPS(){    
    
}
UBX_MESSAGE_TYPE getPacketMessageType (UBX_MSG_CHECKSUM_HEADER pHeader){
UBX_MESSAGE_TYPE msgTypes[1] = {
            {0x01,0x02,0,"NAV-POSLLH"}
          };
return msgTypes[0];

}
2 
tmGPS::UBX_MESSAGE_TYPE

?

3

Will your application code (.ino and/or other .cpp files) be calling the getPacketMessageType() function? If so, the UBX_MESSAGE_TYPE type needs to be public.

4

And, as @anon73444976 pointed out, the type (when used outside of the class definition) will be 'tmGPS::UBX_MESSAGE_TYPE'.

5

It only be used privately by the class. And not from the .ino file

8

Fixed your errors so that it at least compiles.
tmGPS.h:

// YOUR REALLY NEED #INCLUDE GUARDS HERE!!!!!
#include <string>

class tmGPS {
  private:
    struct  UBX_MESSAGE_TYPE {
      unsigned char cls;
      unsigned char id;
      unsigned short length;
      std::string mNemonic;
    } ;

    struct UBX_MSG_CHECKSUM_HEADER {
      unsigned char cls;
      unsigned char id;
      unsigned short length;
    };

    UBX_MESSAGE_TYPE getPacketMessageType(UBX_MSG_CHECKSUM_HEADER pHeader);

  public:
    tmGPS() {}
};

tmGPS.cpp

#include "tmGPS.h"

tmGPS::UBX_MESSAGE_TYPE tmGPS::getPacketMessageType (UBX_MSG_CHECKSUM_HEADER pHeader) {
  UBX_MESSAGE_TYPE msgTypes[1] = {
    {0x01, 0x02, 0, "NAV-POSLLH"}
  };
  return msgTypes[0];
}

I'm not sure what will happen when you try to return the value of a local variable of type UBX_MESSAGE_TYPE that contains a std:string member (since it surely has dynamically allocated data). Hopefully the return value will be copy-constructed (or move-constructed) from your local variable 'msgTypes'.

9

I believe the only problem was the missing scope on the function definition. I don't believe it's needed on the UBX_MESSAGE_TYPE type declarations. The function automatically has the same scope as the struct. This should work:

#include "tmGPS.h"

UBX_MESSAGE_TYPE tmGPS::getPacketMessageType (UBX_MSG_CHECKSUM_HEADER pHeader) {
  UBX_MESSAGE_TYPE msgTypes[1] = {
    {0x01, 0x02, 0, "NAV-POSLLH"}
  };
  return msgTypes[0];
}
10

Well .... also the function was defined with 2 parameters in the .h file and only 1 parameter in the .cpp file.

11

Doesn't compile for me. Code in #8 did.

12

Thank you, thank you, thank you! I tried prefix tmGPS:: to return type and the moved it to the method name, I didn't try add it to both. I did it and all compiles.

tmGPS::UBX_MESSAGE_TYPE tmGPS::getPacketMessageType (...)
13

Hmmmm... That surprises me... Why?

14

Thank you all for your kind help and advice. Amazing that you all came to my assistance instantly. Now on with my learning :slight_smile:

15

Because the type UBX_MESSAGE_TYPE is defined in tmGPS scope.