Streaming

Streaming C++-style Output with Operator <<

Note: Streaming 5 is now Arduino 1.0 compatible.

New users sometimes wonder why the “Arduino language” doesn’t provide the kind of concatenation or streaming operations they have become accustomed to in Java/VB/C#/C++, etc.

// This doesn't work in Arduino.  Too bad.
lcd.print("The button was pressed " + counter + " times");

Meanwhile, experienced programmers chafe at having to synthesize streams with clumsy blocks of repetitive code like this:
lcd.print("GPS #");
lcd.print(gpsno);
lcd.print(" date: ");
lcd.print(day);
lcd.print("-");
lcd.print(month);
lcd.print("-");
lcd.println(year); // ugh!!

The Streaming library gives you the option of compressing those into “insertion style” code that, if not exactly the same, is reminiscent of the concatenation above:
lcd &lt;&lt; "GPS #" &lt;&lt; gpsno &lt;&lt; " date: " &lt;&lt;
    day &lt;&lt; "-" &lt;&lt; month &lt;&lt; "-" &lt;&lt; year &lt;&lt; endl;

This library works for any class that derives from Print:
Serial &lt;&lt; "Counter: " &lt;&lt; counter;
lcd &lt;&lt; "Temp: " &lt;&lt; t.get_temperature() &lt;&lt; " degrees";
my_pstring &lt;&lt; "Hi Mom!" &lt;&lt; endl;

With the new library you can also use formatting manipulators like this:
Serial &lt;&lt; "Byte value: " &lt;&lt; _HEX(b) &lt;&lt; endl;
lcd &lt;&lt; "The key pressed was " &lt;&lt; _BYTE(c) &lt;&lt; endl;

This syntax is familiar to many, is easy to read and learn, and, importantly, consumes no resources. (Because the operator functions are essentially just inline aliases for their print() counterparts, no sketch gets larger or consumes more RAM as a result of their inclusion.)
I hope someday that this simple template will become part of the Arduino core as a stylistic option to writing series of prints. In the meanwhile, I use it in every sketch I build now!
Download
The latest version of Streaming is available at Streaming5.zip.
Version
You can get the current version number of the library by inspecting STREAMING_LIBRARY_VERSION.

Page last updated on July 31, 2024 at 8:06 am

115 Responses → “Streaming”

wea

12 years ago

wow !great library, and very very useful more power to you ! u help a lot of people like
Daniel

12 years ago

hi,
would it be possible to include this snippet in a future release in Streaming.h ?
it only appends a carriage return instead of CR,LF ( as endl) some hardware only want a carriage return as an end of message sentinel and get upset if they get a line feed as well.
”
enum _CarriagReturnCode { crl };

inline Print &operator <<(Print &obj, _CarriagReturnCode arg)
{ obj.print("\r"); return obj; }
"
Mikal

12 years ago

@Daniel,

Good thought–I think about it.

M
matt

12 years ago

I wanna send a command to an rfid reader/writer and i need an explination of how to do it, the data sheet: http://www.elechouse.com/elechouse/images/product/13.56MHZ_RFID_Module/13.56MHZ_RFID_Manual.pdf

Can someone cook up some example code? THANKS GUYS! YOU’RE AWESOME!
Mikal

12 years ago

@matt,

It’s an ordinary 5V TTL Serial device. I think there’s lots of sample code out there for RFID reader/writers, aren’t there?
Arend

12 years ago

:D Really great! They should put this in the standard Arduino environment!
Rob Tillaart

11 years ago

Hi Mikal,

Looks good! A small trick to get a leading zero (e.g. in a time string)

int h = 14;
int m = 6
Serial << ((h<10)?"0":"") << h << ":" << ((m<10)?"0":"") << m << endl;

it would be nice to have something parametrised like

Serial << ZERO(hour,2) << ":" << ZERO(minute,2) << endl;

Serial << ZERO(money, 4) << endl;
Rob Tillaart

11 years ago

addition, to fill output with some char

struct _FILL
{
char ch;
int len;
_FILL(char c, int l): ch(c), len(l)
{}
};

inline Print &operator <<(Print &obj, const _FILL &arg)
{ for (int i=0; i< arg.len; i++) obj.write(arg.ch); return obj; }

examples
Serial << _FILL('=', 20) << endl;

int table[10] = {5,10,4,6,8,12,6,5,3,2};
for (int i=0; i<10; i++)
{
Serial << _FILL('*', table[i]) << endl;
}
Rob Tillaart

11 years ago

see also – http://arduino.cc/forum/index.php/topic,131283.0.html –

struct _TIME
{
uint8_t hour;
uint8_t minu;
uint8_t sec;
_TIME(uint8_t h, uint8_t m, uint8_t s): hour(h), minu(m), sec(s)
{}
};

inline Print &operator <<(Print &obj, const _TIME &arg)
{ obj.print(((arg.hour<10)?"0":"")); obj.print(int(arg.hour));
obj.print(((arg.minu<10)?":0":":")); obj.print(int(arg.minu));
obj.print(((arg.sec<10)?":0":":")); obj.print(int(arg.sec));
return obj; }

Not optimized but might be useful
tony

11 years ago

Hey,

Thanks for this nice library, serial communication works just fine, but i have a problem with printing messages on lcd. Im using LiquidCrystal from arduino standard lib in order to get lcd to work, and yours “steaming” for communicate with it. How can i clear the screen using your library? Also how can i set cursor in custom line/row. In LiquidCrystal im using lcd.clear(), lcd.setCursor (x,y) etc.

Thanks in advance.
tony
Wakt

11 years ago

Good work. I always wondered why something like this wasn’t included in the first place considering how useful and relatively standard it in nowadays.
Albert

11 years ago

I found that << endl is not the same as << "\n". With endl I can't read the serial monitor output to Excel. endl generates an unknown character.
Mikal

11 years ago

Rob–

I quite agree. Thanks for the suggestion.

Mikal
Mikal

11 years ago

@tony,

The Streaming library isn’t smart enough to know about every possible target device. But that’s ok. For lcd, just do lcd.clear() like usual, then use streaming to write to the lcd. lcd << "Hello!";
Mikal

11 years ago

@Albert,

endl in Streaming-land is “\r\n”, which I think is generally more useful. Apparently not in this case, though. I’m surprised Excel doesn’t like it though. Hmm.. Thanks.
Albert

11 years ago

Dear Mikal,
Please can you add examples of setting the digits / precision?
For instance, this works fine:
pString << _FLOAT(floatblabla, 1); // precision = 1 digit

Best regards

Albert van Dalen
Mikal

11 years ago

@Albert,

Good idea…!
omar

11 years ago

Hi, Im having errors while using this library, how do you get it to work after download?

Im trying to print a message followed by a single variable and get this error:
Single_Stepper_Motor_Control:63: error: no match for ‘operator<<' in 'Serial << ("Front Speed: ")'

The syntax Im using is as follows, if Im mistaken please advice:
Serial << "Front Speed: " << time;
Mikal

11 years ago

@omar,

It seems like that should work. Are you including streaming.h?
omar

11 years ago

I copied the library to the libraries of IDE for arduino, dont know if there is any other thing that I should do.
Mikal

11 years ago
I mean, did you add the
```
#include <Streaming.h>
```
line at the top of your code?
omar

11 years ago

No Mikal I forgot that, I included and its working fine thanks.
Marc

11 years ago

When you put the example code for Flash and streaming together into one code. Some functions from each library don’t work anymore (endl, etc…)
why ?
Mikal

11 years ago

@Marc,

Can you give an example?
Anthrolume

11 years ago

Hi Mikal,

Great stuff. I used this on my Anthrolume project, and now I’m refitting that project with a Maple instead of the Arduino Mega I used originally. You’ll be glad to know that Streaming.h works perfectly as-is on the Maple! :-)
omar

11 years ago

Can this library send a clear line or reset line or clear screen to the serial monitor of the arduino IDE?
Frank

11 years ago

Excellent!
I enhanced the library with some of the ideas in the comments
I even stumbled across a small omission – _FLOAT was not in the keywords file
I also enhanced the example sketch
I’ be happy to share what I have so far
a

10 years ago

// This doesn’t work in Arduino. Too bad.
lcd.print(“The button was pressed ” + counter + ” times”);

// However, this does work in Arduino:
lcd.print(“The button was pressed ” + String(counter) + ” times”);
Mikal

10 years ago

@a,

Very true (although you couldn’t do that back when this article was first written).

However, I am not in favor of using Strings in these scenarios. In fact I never use String at all in any of my code. It’s just too unpredictable to use dynamic memory in a processor with 2K of RAM.
Helmi

10 years ago

Nice,
How about using below function :
char buffer[23];

sprintf(buffer,”Time : %d : %d : %d”,hours,minutes,second);

Serial.print(buffer);
Mikal

10 years ago

@Helmi–

sprintf is a great tool, but doesn’t work in two cases I know of. First of all, on avr-gcc the %f formatter for floating point numbers simply isn’t implemented, presumably to save space. Secondly, there are some cases where you actually have to pass a Stream or Print object to a library function and sprintf can’t behave as a Stream object. Thanks.
se

10 years ago

Hello, How would I use streaming to write to an SD card? Thank you, Steve
ElEspanol

10 years ago

Hi, I can not get work this example. I understand it that it stores the result in a String (char? or whatever) instead of printing it to somewhere. Is this correct?

my_pstring << "Hi Mom!" << endl;

So, please, how can I get it work? The other like lcd << "Hi Mom!" << endl; or Serial << "Hi Mom!" << endl; work well
Mikal

10 years ago

Yes, that example should “print” the value “Hi Mom!” to my_pstring. What issues are you having?
ElEspanol

10 years ago
```
#include <Streaming.h>
String my_pstring="";
void setup() {
Serial.begin(9600);
my_pstring << "Hi Mom!" << endl;
Serial.println(my_pstring);
}

void loop() {}
```
Errores:
Arduino: 1.5.7 (Windows XP), Board: “Arduino Mega or Mega 2560, ATmega2560 (Mega 2560)”

sketch_oct03b.ino: In function ‘void setup()’:
sketch_oct03b.ino:6:12: error: no match for ‘operator<<' (operand types are 'String' and 'const char [8]')
sketch_oct03b.ino:6:12: note: candidates are:
In file included from sketch_oct03b.ino:1:0:
D:\Arduino\libraries\Streaming/Streaming.h:33:15: note: template Print& operator<<(Print&, T)
inline Print &operator <<(Print &stream, T arg)
^
D:\Arduino\libraries\Streaming/Streaming.h:33:15: note: template argument deduction/substitution failed:
sketch_oct03b.ino:6:15: note: cannot convert 'my_pstring' (type 'String') to type 'Print&'
In file included from sketch_oct03b.ino:1:0:
D:\Arduino\libraries\Streaming/Streaming.h:54:15: note: Print& operator<<(Print&, const _BYTE_CODE&)
inline Print &operator <<(Print &obj, const _BYTE_CODE &arg)
^
D:\Arduino\libraries\Streaming/Streaming.h:54:15: note: no known conversion for argument 1 from 'String' to 'Print&'
D:\Arduino\libraries\Streaming/Streaming.h:73:15: note: Print& operator<<(Print&, const _BASED&)
inline Print &operator <<(Print &obj, const _BASED &arg)
^
D:\Arduino\libraries\Streaming/Streaming.h:73:15: note: no known conversion for argument 1 from 'String' to 'Print&'
D:\Arduino\libraries\Streaming/Streaming.h:91:15: note: Print& operator<<(Print&, const _FLOAT&)
inline Print &operator <<(Print &obj, const _FLOAT &arg)
^
D:\Arduino\libraries\Streaming/Streaming.h:91:15: note: no known conversion for argument 1 from 'String' to 'Print&'
D:\Arduino\libraries\Streaming/Streaming.h:102:15: note: Print& operator<<(Print&, _EndLineCode)
inline Print &operator <<(Print &obj, _EndLineCode arg)
^
D:\Arduino\libraries\Streaming/Streaming.h:102:15: note: no known conversion for argument 1 from 'String' to 'Print&'
ElEspañol

10 years ago

Got it. The secret was to include the Pstring class

Thx.
Mark

9 years ago

Is there a documentation file showing detailing all of the functionality/formatting/usage? I see the use of “endl”; is there documentation listing this and other key words?
Mikal

9 years ago

@Mark, “endl” is borrowed from C++. It simply means “end of line”. I think that’s about the only “special” formatting stuff in this library.
Adam

9 years ago

I like this library a lot as it provides familiar syntax :) To get it to work under 1.6.4 I had to create a file called “library.properties” and populate it with the following:

name=Streaming
version=5
author=Arduino
maintainer=Mikal Hart
sentence=Streaming C++-style Output with Operator <<
paragraph=Streaming C++-style Output with Operator <<
category=Language
url=http://arduiniana.org/libraries/streaming/
architectures=*

Hope this helps, and thanks Mikal! :)

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