ESP32S2 Multiple definition of `USBSerial' but it is only defined once in the class

Projects Programming
1

Are there some additional defines which i can not see because if i just use the main.cpp like this:

#include "USB.h"
#include "Arduino.h"

#if ARDUINO_USB_CDC_ON_BOOT
#define HWSerial Serial0
#define USBSerial Serial
#else
#define HWSerial Serial
USBCDC USBSerial;
#endif
// HWSerial = buildin UART in developmentboard
// USBSerial = Use D+ and D- on the esp32S2 as serial

void setup()
{
    HWSerial.begin(115200);
    HWSerial.setDebugOutput(true);

    USBSerial.begin();
    USB.begin();
}

void loop()
{
    USBSerial.println("Message from the USB port");
    delay(2000);
}

Everthing works but when I use:

#if ARDUINO_USB_CDC_ON_BOOT
#define HWSerial Serial0
#define USBSerial Serial
#else
#define HWSerial Serial
USBCDC USBSerial;
#endif

In a class I get a

multiple definition of `USBSerial';

error.
main.cpp:

#include "USBCommunication.h"

USBCommunication com;
void messageListener(String message)
{
    com.sendMessage("Got message", "PING");
}

void setup()
{
    com.setMessageListener(messageListener);
    com.initCommunication();
    com.startMessageListener();
}

void loop()
{
    // Serial.println("Testmessage");
    com.sendMessage("Message from the USB port", "MESSAGE");
    delay(2000);
}

USBCommunication.h

#include "Communication.h"
#include <Arduino.h>
#include "USB.h"
#pragma once

// ########### Causes problems ################
#if ARDUINO_USB_CDC_ON_BOOT
#define HWSerial Serial0
#define USBSerial Serial
#else
#define HWSerial Serial
USBCDC USBSerial;
#endif
// ############################################


class USBCommunication : public Communication
{
public:
  USBCommunication();
  ~USBCommunication();
  int initCommunication();
  // Becarefull when you call this methode. This will stop all serial communications.
  int stopCommunication();
  int sendMessage(String message,String label);
  int checkForMessages();

private:

};

USBCommunication.cpp:

#include "USBCommunication.h"

USBCommunication::USBCommunication()
{
}

USBCommunication::~USBCommunication()
{
}

int USBCommunication::initCommunication()
{
    HWSerial.begin(115200);
    HWSerial.setDebugOutput(true);
    USBSerial.begin();
    USB.begin();

    USBSerial.begin();
    USB.begin();
    return 0;
}
int USBCommunication::stopCommunication()
{
    USBSerial.end();
    return 0;
}
int USBCommunication::sendMessage(String message,String label)
{
    USBSerial.print("["+label+"]");
    USBSerial.println(message);
    return 0;
}

int USBCommunication::checkForMessages()
{
    while(USBSerial.available())
    {
        this->processMessage(USBSerial.readStringUntil('\n'));
    }
    return 0;
}

(files as full example jqEgewqP)

(The same error happens in the arduion IDE and PlatformIO)

Does someone know more about this? Is that a bug or do in need other defines?

2

The problem is unrelated to classes:

This is a variable definition. You shouldn't have (non-inline) function or variable definitions in header files. Mark it extern in the header and move the definition to an implementation file (.cpp).

3

Can you please show me how I should do that?

Mark it extern in the header and move the definition to an implementation file (.cpp).

What is "it" in this context, do you mean USBCDC?

4

No, “it” is the global USBSerial variable.

Headers should only declare global variables, not define them. See chapter 6 of learncpp.com for more details, e.g. https://www.learncpp.com/cpp-tutorial/scope-duration-and-linkage-summary/

Somefile.hpp

#pragma once

#if ARDUINO_USB_CDC_ON_BOOT
#define HWSerial Serial0
#define USBSerial Serial
#else
#define HWSerial Serial
extern USBCDC USBSerial; // declaration
#endif

Somefile.cpp

#include "Somefile.hpp"

#if !ARDUINO_USB_CDC_ON_BOOT
USBCDC USBSerial; // definition
#endif
5

Thank you that solved my problem.

6

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