C++ array of pointers to objects

I was driving multiple TFT LCDs on the same microcontroller. Each LCD had its own instance and I needed an easy method of iterate through all of them.

The platform I used is a ST Nucleo F411RE board, the programming enviroment is mbed and the TFT LCDs are 2.2 inch ILI9341 display.

By using a single screen, the code could look like this:

	// https://ee-programming-notepad.blogspot.com/2016/10/c-array-of-pointers-to-objects.html
	#include "mbed.h"
	#include "ILI9340_Driver.h"
	#define LCD_MOSI D11
	#define LCD_MISO D12
	#define LCD_SCK D13
	#define LCD_CS D5
	#define LCD_RST D3
	#define LCD_DC D7
	ILI9340_Display lcd(LCD_MOSI, LCD_MISO, LCD_SCK, LCD_CS, LCD_RST, LCD_DC); // MOSI, MISO, SCK, CS, RST, D/C
	int main() {
	lcd.DispInit();
	lcd.SetRotation(0);
	lcd.FillScreen(ILI9340_BLUE);
	lcd.DrawString("Test", 0, 0, 2, ILI9340_WHITE); // draw a text with 8px font
	}

view raw single_lcd_test.cpp hosted with ❤ by GitHub

On the other hand, by using multiple screens, the code could look like this:

	// https://ee-programming-notepad.blogspot.com/2016/10/c-array-of-pointers-to-objects.html
	#include "mbed.h"
	#include "ILI9340_Driver.h"
	#define LCD_MOSI D11
	#define LCD_MISO D12
	#define LCD_SCK D13
	#define LCD_DC D7
	#define LCD1_RST D3
	#define LCD1_CS D5
	#define LCD2_RST A1
	#define LCD2_CS A0
	#define LCD_NO_SCREENS 2
	ILI9340_Display * tft_lcds[LCD_NO_SCREENS];
	int main() {
	char i = 0;
	PinName cs_pin, rst_pin;
	ILI9340_Display * tft_lcd; // array of pointers to objects
	while (i < LCD_NO_SCREENS) // iterate the screens
	{
	switch (i)
	{
	case 0: // first screen
	cs_pin = LCD1_CS;
	rst_pin = LCD1_RST;
	break;
	case 1: // second screen
	cs_pin = LCD2_CS;
	rst_pin = LCD2_RST;
	break;
	}
	// instantiate the LCD class
	tft_lcd = new ILI9340_Display(LCD_MOSI, LCD_MISO, LCD_SCK, cs_pin, rst_pin, LCD_DC); // MOSI, MISO, SCK, CS, RST, D/C
	tft_lcd->DispInit();
	tft_lcd->SetRotation(0);
	tft_lcd->FillScreen(ILI9340_BLUE);
	// push the new instance to the array of pointers
	tft_lcds[i] = tft_lcd;
	i++;
	}
	// ... code ...
	wait(2);
	// later on, display some text on LCD
	i = 0;
	while (i < LCD_NO_SCREENS)
	{
	tft_lcds[i]->FillScreen(ILI9340_RED);
	char buff[20];
	sprintf(buff, "Loading %d...", i);
	tft_lcds[i]->DrawString(buff, 0, 0, 2, ILI9340_WHITE); // draw a text with 8px font
	i++;
	}
	}

view raw multiple_lcd_test.cpp hosted with ❤ by GitHub

The code is not elegant, but it gets the job done.
Note that the LCDs RST and CS pins need to be individually connected to the microcontroller.

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Reference: www.java2s.com