Send String to a function inside a class

Question

I made a little class for handling menus. When creating a new instance, I pass a reference to the oled object made in main.cpp. Yet when I want to render a string using a variable, it throws an error. But I can pass a string directly to the render function with no problems. See comments in the code for what is working and what is not.

#include "Arduino.h"
#include "U8glib.h"
#pragma once

class Menu {
  U8GLIB_SSD1306_128X64& oled;

  public:
    Menu(U8GLIB_SSD1306_128X64& oled): oled(oled) {
      this->oled = oled;
    };
    void render() {
      this->oled.firstPage();
      do {
        String text = "test2";
        this->oled.setFont(u8g_font_unifont);
        this->oled.setPrintPos(0, 20);
        this->oled.drawStr(text); // not working
        this->oled.drawStr(text.c_str()); // not working
        this->oled.drawStr("works"); // works
      } while (this->oled.nextPage());
    }
  };

In the case of this->oled.drawStr(text); the error is:

error: no matching function for call to 'U8GLIB_SSD1306_128X64::drawStr(String&)

In case of this->oled.drawStr(text.c_str()) the error is:

error: no matching function for call to 'U8GLIB_SSD1306_128X64::drawStr(const char*)

How I create the instance in main.cpp:

U8GLIB_SSD1306_128X64 oled(U8G_I2C_OPT_NONE);
Menu menu(oled);
menu.render();

I can find no mention of a drawStr function in the current U8glib library that takes only one parameter. What version are you using and where did you get it? — Majenko
– Majenko, Commented Sep 24, 2017 at 10:44
I udated to u8g2 lib, passed 3 parameters (int int c_str) and I'm still getting the same error — Martin Velinský
– Martin Velinský, Commented Sep 24, 2017 at 12:39
@MartinVelinský if you updated it, then edit the question and ADD the new code, otherwise it is impossible to properly answer — frarugi87
– frarugi87, Commented Sep 25, 2017 at 15:59

dda · Accepted Answer · 2017-09-24 13:14:27Z

2

Try with the new version, U8g2lib.

With that version, you can write code like this:

String t1 = "Grow";
String t2 = "Room";
u8g2.firstPage();
do {
  u8g2.setFont(u8g2_font_logisoso24_tf);
  u8g2.drawStr(32, 24, t1.c_str());
  u8g2.drawStr(32, 60, t2.c_str());
} while(u8g2.nextPage());

edited Sep 24, 2017 at 13:14

dda

1,5951 gold badge12 silver badges18 bronze badges

answered Sep 24, 2017 at 10:42

user31481

even with a u8g2 lib, I'm still getting the same compile error

Martin Velinský
– Martin Velinský

2017-09-24 12:38:51 +00:00
Commented Sep 24, 2017 at 12:38
2

Post a complete updated sketch with u8g2lib to better resolve.

user31481
– user31481

2017-09-24 12:47:42 +00:00
Commented Sep 24, 2017 at 12:47

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Delta_G · Accepted Answer · 2017-09-24 23:02:20Z

0

Forget the String class. It wastes memory on a system that is already constrained by memory. Define your strings as const char * and you won't have any problems.

const char* t1 = "Grow";
const char* t2 = "Room";
u8g2.firstPage();
do {
  u8g2.setFont(u8g2_font_logisoso24_tf);
  u8g2.drawStr(32, 24, t1);
  u8g2.drawStr(32, 60, t2);
} while(u8g2.nextPage());

answered Sep 24, 2017 at 23:02

Delta_G

3,3912 gold badges13 silver badges24 bronze badges

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