2D pointer array of structure

Using Arduino Programming Questions
#1

Hi everyone,

i have a problem with a 2D pointer array. I’m trying to code a menu for a I2C Display. The idea is that each column of my 2D Pointer Array (“matrix”) represents a individual menu with entries on its own. Each entry should consist of a structure that contains the displayed text and a number, that corresponds to the next menu he is supposed to jump to.

So i tried this, but i get nonsensical output on the display:

#include <SPI.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

#define OLED_RESET 4
Adafruit_SSD1306 display(OLED_RESET);

class Disp_menu
{
  public:
  Disp_menu();
  void addElement(int layer,char title,int link);
  void delElement();
  void draw();
  private:
  typedef struct{
    char title[20];
    int link;
    } element;
  element **_menu;
};
Disp_menu::Disp_menu(){
  _menu = (element**) calloc(1,sizeof(element*));
  element el1 = {"Hallo",0};
  _menu[0][0] = el1;
}
void Disp_menu::draw(){
  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(WHITE);
  display.setCursor(0,0);
  display.println(_menu[0][0].title);
  Serial.println(_menu[0][0].title);
  display.display();
  delay(2000);
}
void setup() {
  Serial.begin(9600);
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
  display.display();
  delay(2000);
  menu.draw();
}
void loop() {
  // put your main code here, to run repeatedly:
}

What am i missing? I would be thankful to any kind of help

#2

I don’t see the declaration for the variable menu. Does that even compile?

Where do you put items into the menu? It looks like there is nothing to display.

#3