i suck at arduino code

[kr...@sleepingplanet.com]

ok,

i have an arduino sketch that combine the one wire library, the dallas temperature monitor library and u8graphics library.

 

i want the oled screen to show the temperature in the kids room

this section of code:

void draw(void) {
  // graphic commands to redraw the complete screen should be placed here  
  u8g.drawStr( 0, 10, "inside"); 
  u8g.drawStr( 0, 28, "outside");
  u8g.drawStr( 0, 46, "kids");
  u8g.drawStr( 0, 64, "time");
}

works fine, but when i begin to use a variable (that will have the actual temperature)

void draw(void) {
  // graphic commands to redraw the complete screen should be placed here  
  String line1 = "inside";
  u8g.drawStr( 0, 10, line1); 
  u8g.drawStr( 0, 28, "outside");
  u8g.drawStr( 0, 46, "kids");
  u8g.drawStr( 0, 64, "time");
}

i get the error

Arduino/libraries/U8glib/U8glib.h:201:16: note:   no known conversion for argument 3 from 'String' to 'const __FlashStringHelper*'
no matching function for call to 'U8GLIB_SSD1306_128X64::drawStr(int, int, String&)'

what i understand is the "inside" bit i assumed is a String but is in fact a FlashStringHelper? and the two arn't compatible

what i want is to create a string like this

String line1 = string("inside " + printTemperature(localThermometer)));

[kr...@sleepingplanet.com]

alrigth i think i was getting confused about the string variable, apparently i should be using char

or calling the u8g.print function when i'm using strings

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[Patrick Barnes]

Yeah, be aware of the big differences between a literal string and a string that you reference or build at run-time.

In many cases they're even stored in entirely different sections of memory (program memory vs ram)

[Paul]

Would line1.c_str() do the trick? It's hard to tell what is String in this context since you've omitted the includes, but chances are it's inherited from the STL string.
Anyway, there must be an accessor to pull the underlying char* representation.

Disclaimer: I last used real C++ about 6 years ago.

[Paul]

Ah, so arduino sdk has its own String, which in turn offers c_str(): https://www.arduino.cc/en/Reference/StringObject

[Ada Lim]

On Mon, Oct 26, 2015 at 7:34 PM, Patrick Barnes <mrt...@gmail.com> wrote:
> Yeah, be aware of the big differences between a literal string and a string
> that you reference or build at run-time.
> In many cases they're even stored in entirely different sections of memory
> (program memory vs ram)

Also beware of the difference between a string and a String.

u8g's print understands the same things as the arduino print, viz.
String, char*, char/uchar, int/uint, long/ulong, and double. u8g's
drawStr only understands char* (which is what most C programmers refer
to as a string). so paul's suggestion of c_str should work.

also, can someone tell me why this bit of code is legal:

void print(long, int = DEC);
void print(unsigned long, int = DEC);
void print(double, int = 2);

I didn't think you were allowed to use keywords as parameter names.

(also, int = 2 is very disgusting. Arduino Quality Software.)

-A

[Matt Callow]

I don't see any parameter names, only parameter types.

Matt

[Ada Lim]

On Tue, Oct 27, 2015 at 3:18 AM, Matt Callow <matt....@gmail.com> wrote:
>> I didn't think you were allowed to use keywords as parameter names.
> I don't see any parameter names, only parameter types.

Right. I've been pythoning for too long.

-A

[kr...@sleepingplanet.com]

thanks!

i ended up using u8g print function, which as you said is the same as serial.print and i already had that working so all was good.

personally, i always find it a bit depressing discovering how much I don't know about something (in this case programming).

it's great acheiving something and i should focus on the the small wins. but yeah, just adding a variable to a string to make a new string i didn't think would take me 2 hours.

[Patrick Barnes]

On 27/10/2015 1:55 AM, Ada Lim wrote:

also, can someone tell me why this bit of code is legal:

    void print(long, int = DEC);
    void print(unsigned long, int = DEC);
    void print(double, int = 2);

I didn't think you were allowed to use keywords as parameter names.

(also, int = 2 is very disgusting.  Arduino Quality Software.)

-A

Those are function definitions / prototypes.

In C, the .h file just defines the parameter and return types, eg void print(long, int);
Then the .c (or .ino) file has the function definition eg void print(long a, int b) { .... }

In Arduino-flavoured C - which I think has a few C++ish things in it - the 'type = value' in the prototype defines a default value.
So you could call print(10) or print(10, DEC) and it'd do the same thing.
From the context, I'm guessing that's the base that print uses, decimal, octal etc.

Yes using 'int = 2' is pretty terrible.

[Paul]

Also beware of the difference between a string and a String.

As in "string" doesn't actually exist in the Arduino world and using it in context of types is pretty much always ambiguous?