Multiple files issue resulting in Multiple Definitions

Using Arduino Programming Questions
1

Hi,

I am working on a project that is making use of the NTPClient library to get the current date. I am working on a NodeMCU ESP32, so have connected it to the WiFi. When testing the library out, I worked with one file and everything went well. I was able to extract and print the current date. Now, I am trying to implement the same thing into my project, however, I am running into an issue where the library is being defined multiple times. I can't seem to figure out where to place the definitions and initialisations. I have 5 files. Here is my project structure:

  • cros.ino :
    This file is the one I upload to the chip. It includes 3 other files.
#include "cros_core.h"
#include "cros_constants.h"
#include "cros_types.h"

I define a class that has been created in cros_core.h:

CCrowboxCore g_crOSCore;

And within the setup() function, I call:
g_crOSCore.Setup();
Which has the logic of the program.

  • cros_core.h :
    This file is defines everything and also sets up a class. The definitions I have included for example are:
#include <ESP32Servo.h>
#include <WiFi.h> 
#include <FirebaseESP32.h>
#include <NTPClient.h>
#include <WiFiUdp.h>

In this file, I also then try to initialise the NTPClient, as I would have done if everything were in one file:

WiFiUDP ntpUDP;
NTPClient timeClient(ntpUDP);

There is also a class set up here which looks something like:

class CCrowboxCore
{
public:
    CCrowboxCore();
    void Setup();
    void Loop();

public:
    void DebugPrint( const char *pString );
    void ReportSystemError( cros_error_code_t errorCode );
    
    //--------------------------------------
    // Public Accessor methods
    //--------------------------------------
    cros_time_t GetUptimeSeconds();
    bool        IsABirdOnThePerch();
    cros_time_t HowLongHasBirdBeenHere();
    cros_time_t HowLongHasBirdBeenGone();

And more...

  • cros_core.cpp :
    In here, I have the code for the program. In the setup() function of this class, I begin the NTPClient:
timeClient.begin();
timeClient.setTimeOffset(3600);

I then make use of the timeClient in the class loop() function.

The error I am getting from this is:

sketch\cros_core.cpp.o:(.bss.timeClient+0x0): multiple definition of `timeClient'
sketch\cros.ino.cpp.o:(.bss.timeClient+0x0): first defined here
sketch\cros_core.cpp.o:(.bss.ntpUDP+0x0): multiple definition of `ntpUDP'
sketch\cros.ino.cpp.o:(.bss.ntpUDP+0x0): first defined here
collect2.exe: error: ld returned 1 exit status

Where should I be defining and initialising:

#include <NTPClient.h>
#include <WiFiUdp.h>

And

WiFiUDP ntpUDP;
NTPClient timeClient(ntpUDP);

Appreciate the help!

2

Post the entire error message.

3

Also, post a complete code, preferably an MRE.

Trying to mentally piece together all your incomplete snippets into a coherent picture is more effort than I'm willing to expend.

4

Hi! The only left out line is:

Error compiling for board DOIT ESP32 DEVKIT V1.
5

You scrolled all the way up to the top of the error message window? That's not much info to go on. Good luck to you.

6

Yes. Do you know how I might get a more detailed error message?

Not sure if you missed it in the post but this was the error message:

sketch\cros_core.cpp.o:(.bss.timeClient+0x0): multiple definition of `timeClient'
sketch\cros.ino.cpp.o:(.bss.timeClient+0x0): first defined here
sketch\cros_core.cpp.o:(.bss.ntpUDP+0x0): multiple definition of `ntpUDP'
sketch\cros.ino.cpp.o:(.bss.ntpUDP+0x0): first defined here
collect2.exe: error: ld returned 1 exit status
Error compiling for board DOIT ESP32 DEVKIT V1.
7

I fixed the issue by moving:

#include <NTPClient.h>
#include <WiFiUdp.h>

And

WiFiUDP ntpUDP;
NTPClient timeClient(ntpUDP);

To the .cpp file instead of the .h file.

8

That's the problem. You can't define global variables in a .h file that is included in two places:

  1. cros.ino
  2. cros_core.cpp

To fix it, change cros_core.h to contain:

extern WiFiUDP ntpUDP;
extern NTPClient timeClient(ntpUDP);

Then pick EITHER cros.ino or cros_core.cpp to define the two globals. The 'extern' declaration will let both source files use the global objects but you can only define them in one.

1 Like
9

That makes a lot of sense, thank you!

10

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