What does it mean?

Using Arduino Programming Questions
1

Hello 2 Questions:

If I pass a string its done like Serial.print("ABC");
But sometimes I found functions or such where the String is written like this ('ABC').

Why is sometimes " and sometimes ' used?
Couldn't find anything in the reference and can't remember from back the as I was programming C.

For passing AT commands I would normally use
Serial. print("AT....");
But sometimes in the net I find:
Serial. print(F("AT....") );

So what does this F function do here?

2

Gorkde:
If I pass a string its done like Serial.print("ABC");

https://www.google.com/search?q=c%2B%2B+string+constant

But sometimes I found functions or such where the String is written like this ('ABC').

https://www.google.com/search?q=c%2B%2B+character+constant

Why is sometimes " and sometimes ' used?

Quotes for strings. Apostrophes for characters.

So what does this F function do here?

https://www.google.com/search?q=arduino+f-macro

Reduce the amount of SRAM used by the sketch.

3

Thanks!

Yeah I read that but want to understand how, therefore what is the f() doing, ist there any reference where I can read about?

4

F() is just a macro that forces a cast into the string, which ensures the string stays in flash, and allows the selection of the correct method to read it from there and print it.

5

Apostrophes for characters.

But only for single characters.

6

UKHeliBob:
But only for single characters.

Nope.

int multichar = 'AB'; is perfectly legal, as is long multichar = 'name';
Just be careful what you do with them.

7

AWOL:

long multichar = 'name';

Just be careful what you do with them.

Type of 'name' is int, why do you put it in a long?

8

is perfectly legal

Legal in the sense that it is accepted by the compiler, but not a habit to get into I think. Can you suggest a legitimate reason for using a multi character char variable ?

9

In the past, I've used it on low-memory architectures (not unlike the AVR) to avoid the relatively high overhead of a string's terminating null, when storing simple commands or mnemonics.

10

oqibidipo:
Type of 'name' is int, why do you put it in a long?

On some architectures, long and int are the same size.

11

I've used it on low-memory architectures (not unlike the AVR) to avoid the relatively high overhead of a string's terminating null,

You know that you are short of memory when literally every byte counts.
Thanks for the example.

12

UKHeliBob:
You know that you are short of memory when literally every byte counts.
Thanks for the example.

I did once hear of a commercial system (I think it was an alarm system, but it's over 30 years ago) based on a Z-80 that had no RAM, but relied solely on the registers and pre-compiled stack return addreseses.
Personally, I think that was going a bit too far, even back then, but sometimes extra costs are critical.

13

UKHeliBob:
Can you suggest a legitimate reason for using a multi character char variable ?

Magic numbers.

14