Declaring hd44780_I2Cexp in header

[dromer]

I've been trying to use the library in a platformio project and ran into some issues when refactoring my main.cpp to various submodules. I think because of the autoconfigure method I am unable to declare an lcd object in my header file.

multiple definition of `hd44780_I2Cexp::AutoInst'

When I disable the 3 lines with AutoInst (declaration, use and definition) in hd44780_I2Cexp.h I am able to declare my screen (I use manual addressing in the definition).

How should I be able to declare the instance without wrecking the library? :)

[bperrybap]

Yeah, static class variables are messy. I probably need to do some changes to the code to make this work correctly when included in multiple modules. Can you provide a simplified example of some code that is having the issue, so that I replicate the issue?

[dromer]

Ok something like this (btw I have to include Wire.h for the lib to work like this):

main.cpp:

#include <function.h>

extern hd44780_I2Cexp lcd;

void setup(){
    lcd.begin(2, 16);
}
void loop(){}

function.h:

#include <Wire.h>
#include <hd44780.h>
#include <hd44780ioClass/hd44780_I2Cexp.h>

extern hd44780_I2Cexp lcd;

function.cpp:

#include <function.h>

hd44780_I2Cexp lcd(0x3F);

Results in:

Compiling .pioenvs/d1_mini/src/function.o
Linking .pioenvs/d1_mini/firmware.elf
.pioenvs/d1_mini/src/main.o:(.bss._ZN14hd44780_I2Cexp8AutoInstE+0x0): multiple definition of `hd44780_I2Cexp::AutoInst'
.pioenvs/d1_mini/src/function.o:(.bss._ZN14hd44780_I2Cexp8AutoInstE+0x0): first defined here
collect2: error: ld returned 1 exit status
*** [.pioenvs/d1_mini/firmware.elf] Error 1

[bperrybap]

This is an issue in the library due to the way I use the header and the static variable declaration. static class variables can be a PITA in C++ Not quite sure yet how I'm going to fix this. As long as you only are using a single instance or are not using auto locate with multiple instances you can work around it by:

• deleting the static definition at the bottom of the class

  uint8_t hd44780_I2Cexp::AutoInst; // define the static auto instance variable

• removing static from the declaration to turn it into a definition. change this

  static uint8_t AutoInst; // declaration only, definition is outside class

  to this

  uint8_t AutoInst; // declaration only, definition is outside class

After that patch, you will still be able to auto locate the i2c address of the backpack when using a single instance. And you can use multiple instances, but when using multiple instances, you must create each lcd object using a specified address.

In the mean time, I'll work on fixing the code to work correctly when using multiple modules.

[dromer]

I do not use the autolocate feature. This didn't work in my setup. Maybe because I have other I2C devices on the bus, non-hd44780 expander type.

[bperrybap]

Please open another issue for this. Autolocate should work as long as there are no other PCF8574 or MCP23008 devices on the bus that are not connected to hd44780 LCDs.

[dromer]

Sure. However I do not mind using a specific address. My main issue is with not being able to declare the lcd object in my headers, but your suggestion on that works here. Maybe I will temporarily keep a fork with these changes that I can use in my projects until there is a permanent solution for this.

[bperrybap]

What I'll probably do for this static variable issue is put something in quickly to resolve it. Then take a bit more time to work out a more elegant permanent fix.

[dromer]

Cool, will look forward to your commit :)

[bperrybap]

Can you try out this patch to make sure it works for your environment? comment out/remove the the existing declaration and definition for AutoInst in the header file. And then add a static declaration to ioinit() like this:

int ioinit()
{
int status = 0;
static uint8_t AutoInst;

This should allow everything to work without creating multiple definitions for the AutoInst variable.

--- bill

[dromer]

You mean like so?

301c301
< static uint8_t AutoInst; // declaration only, definition is outside class
---
> //static uint8_t AutoInst; // declaration only, definition is outside class
329a330
> static uint8_t AutoInst;
1147c1148
< uint8_t hd44780_I2Cexp::AutoInst; // define the static auto instance variable
---
> //uint8_t hd44780_I2Cexp::AutoInst; // define the static auto instance variable

This seems to work fine indeed.

[bperrybap]

Exactly. I'll create a new release later this evening with this patch and a few other minor updates.

[dromer]

Cool, I'll close the issue then :)

[bperrybap]

Work around for this issue is in release 0.8.4