Converting an integer into a const char*

Projects General Guidance
1

Hi Guys
I was trying to make a clock using a graphical LCD screen because I wanted to put animations on there. The screen I'm using is a DOGL128 and I am using a DS1307 RTC to keep the time. The library which comes with the screen has a string function where you can output text to the string, however it requires a const char in the parameter for the text and I wanted to be able to read the time from the chip and output it but I don't know how to convert integers into a const char.
Here is the link to the library I'm using --> http://www.lcd-module.com/support/application-note/arduino-meets-ea-dog.html It is the second link on the page

I would appreciate any help. Thanks

2

Without your code, we can only guess at what's wrong.

Be sure to read this, especially Step 7, when you Modify your post to include your code in between [code]...[/code] tags.

My guess is that you have an integer of some kind, but the library only takes char *. If that's the case, then something like this would work:

  char buf[12];
  lcd.string( col, page, font, itoa( value, buf, 10 ) );

Description of the itoa function (and many others you should know) is here. If that's not what you're trying to do, I just wasted my time guessing without your code.

Cheers,
/dev

3

Here is the code I have so far

#include <dog_7565R.h>
#include <font_16x32nums.h>
#include <font_6x8.h>
#include <font_8x16.h>
#include <font_8x8.h>
#include <logo_BLH.h>
#include <logo_small_BLH.h>

#include <Wire.h>
#include <Time.h>
#include <DS1307RTC.h>
dog_7565R DOG;
const int COMDATA = A0; //Pin 23 on ATMEGA328
const int SERIAL_IN = 1; //Pin 3 on ATMEGA328
const int LCD_DISP_RES = 3; //Pin 5 on ATMEGA328
const int LCD_DISP_SELECT = 10; //Pin 16 on ATMEGA328
const int SERIAL_CLK = 13; //Pin 19 on ATMEGA328

const int p_cs = LCD_DISP_SELECT;
const int p_si = SERIAL_IN;
const int p_clk = SERIAL_CLK;
const int p_a0 = COMDATA;
const int p_res = LCD_DISP_RES;
char T_HOURSONE[5]; //= String("hi");
void setup() {
// put your setup code here, to run once:
DOG.initialize(p_cs, p_si, p_clk, p_a0, p_res,DOGL128);
DOG.clear();
}

void loop() {
// put your main code here, to run repeatedly:
time_t t = 1457848800;
RTC.set(t);
//T_HOURS = hour(t);
//minutes = minute(t);
T_HOURSONE[5] = char(char(hour(t),DEC) + ":" + char(minute(t),DEC));
//char T_HOURSTWO[] = "hi";
DOG.string(25, 3, font_8x16,T_HOURSONE);
}

4 
char(minute(t),DEC))

Do you have a clue what that is doing? I didn't think so.

Misusing the comma operator that way, you are effectively casting 10 to a char. Why do you want to do that?

char(char(hour(t),DEC)

Again, you are casting 10 to a char.

Then, you add 10 + ':' + 10, and cast the sum as a char.

Just because Serial.print(minute(t), DEC) does something does NOT mean that you can remove the Serial.print( and ) and have the same thing happen.

5

Something like:

char buf[50];
void loop()
{
  sprintf(buf,"%2d:%02d",hour,minute);
  lcd.string(25,3,font_8x16,buf);
}

The key is %02d. It formats an integer into a string with up to 2 digit numbers so if you have 2:05pm, then the 5 will be output into 05, what we expect.

6

PaulS - If you read what I said in my original post, I have to cast it into a const char* but I only know how to convert it into a char. I have to cast it into a const char* because that is the type which is required by the function DOG.string() in the last parameter

7

Thank you so much liudr for enlightening me to the serial print function. It worked!