C ++多重继承，何时没有多重定义？

Question

I'm implementing hardware drivers for an embedded C/C++ project, and trying to make things a bit more flexible for future projects.

I have the vast majority of the work done in LCD.hpp/LCD.cpp, where there's a class that has five virtual functions. Four of these are for twiddling GPIO pins and sending SPI messages, and the fifth is for implementing various fonts. A shortened class declaration is as follows:

//LCD.hpp
#include <cstdint>

#ifndef LCD_HPP
#define LCD_HPP
class LCD {
    public:
        virtual void write_character(char what) = 0; //Stores data into a buffer in LCD through another function
    protected:
        virtual void SPI_TX(uint8_t *TXData, uint8_t length, bool ToBeContinued) = 0;
        virtual void update_RST(bool pinstate) = 0;
        virtual void update_DC(bool pinstate) = 0;
        virtual void update_backlight(uint8_t brightness) = 0;
};
#endif

Moving on, I implemented a font-printing write_character as such.

//LCD_FixedWidth.hpp
#include <cstdint>
#include "LCD.hpp"

#ifndef LCD_FIXEDWIDTH_HPP
#define LCD_FIXEDWIDTH_HPP
class LCD_FixedWidth : virtual public LCD {
    public:
        void write_character(char what);
};
#endif

Now it's time for the various hardware bits.

//LCD_hardware.hpp
#include <cstdint>
#include "LCD.hpp"
#include "LCD_FixedWidth.hpp"

#ifndef LCD_HARDWARE_HPP
#define LCD_HARDWARE_HPP
class LCD_hardware : virtual public LCD {
    protected:
        void SPI_TX(uint8_t *TXData, uint8_t length, bool ToBeContinued);
        void update_RST(bool pinstate);
        void update_DC(bool pinstate);
        void update_backlight(uint8_t brightness);
};

And then a class to tie it all together, still in LCD_hardware.hpp...

class LCD_meta : public LCD_hardware, public LCD_FixedWidth {
    public:
        void write_character(char what) { LCD_FixedWidth::write_character(what); };
    protected:
        void SPI_TX(uint8_t *TXData, uint8_t length, bool ToBeContinued) { LCD_hardware::SPI_TX(TXData, length, ToBeContinued); };
        void update_RST(bool pinstate) { LCD_hardware::update_RST(pinstate); };
        void update_DC(bool pinstate) { LCD_hardware::update_DC(pinstate); };
        void update_backlight(uint8_t brightness) { LCD_hardware::update_backlight(brightness); };
};
#endif

And for all of this, I get a multiple definition of LCD_FixedWidth::write_character(char) error. Anybody see anything I'm missing here? All of my headers are guarded properly, and I can only see one implementation of write_character...

Answer 1

This was caused by having LCD_meta and LCD_hardware in the same header file. The code for the LCD_hardware functions was in an implementation file, so the LCD_meta class didn't actually have those functions defined yet... One class per file!