C: string manipulations and Arduino

Question

I'm learning to program in Arduino and, as far as I understand it, it uses the C language (please correct me if I'm wrong).

I'm a senior in JavaScript and PHP, and now I'm having hard time with simple stuff like string handling.

If in JavaScript I have

var c = 33;
var myString = "hello" + c;
alert(myString); //---> hello33

how does it work in C/Arduino?

It's probably best to get [a good book](http://stackoverflow.com/questions/562303/the-definitive-c-book-guide-and-list), rather than trying to learn the language from scratch by asking questions on SO... — Oliver Charlesworth, Apr 08 '12 at 02:00
Specifically, learn about a languages that have stronger typing than JS and PHP. — dreamlax, Apr 08 '12 at 02:10
No, it uses [Processing](https://en.wikipedia.org/wiki/Processing_%28programming_language%29) which is similar to C++ and Java — Eelvex, Apr 08 '12 at 02:35
No, it uses Wiring, which I believe steals the IDE from Processing but uses simplified C++ as the underlying language :-) — paxdiablo, Apr 08 '12 at 03:25
C++. That's all. The Arduino website hides that, but it is true C++ with a real C++ compiler (avr-gcc). Nothing to do with Processing (which is Java based). — Vincent Hiribarren, Apr 08 '12 at 18:09
@Eelvex: The first three paragraphs of Wikipia [Arduino](http://en.wikipedia.org/wiki/Arduino) and my own experience support paxdiablo and Vincent - it is basically C++ with some added gimmicks. — A.H., Apr 09 '12 at 09:42

paxdiablo · Accepted Answer · 2012-04-08T02:51:28.113

3

In C, you would do something like:

char buff[100]; // needs to be large enough.
int c = 33;
sprintf (buff, "hello%d", c); // may want a space after hello

// Now do something with buff.

C is a language where you need to manage some low-level details yourself. There's no automatically expanding string type in the base language/library although no doubt there are some good third-party ones around ("better strings", for example, since it doesn't drag in a lot of other stuff you don't want, particularly important in the embedded space).

edited Apr 08 '12 at 02:51

answered Apr 08 '12 at 02:15

paxdiablo

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+1. Not sure if `snprintf` is available on Arduino but if it is, it can be used to ensure you don't use more `char` than you're supposed to. – dreamlax Apr 08 '12 at 02:18
1

Should not it be `"hello%d"`? – asaelr Apr 08 '12 at 02:19
Yes, I thought I'd format it a little better but I'll change it back for accuracy (with a note). – paxdiablo Apr 08 '12 at 02:51
@dreamlax: yes it is, snprintf is available if you add the stdio.h header, as it is included with components from avr-gcc. – Vincent Hiribarren Apr 08 '12 at 18:22

tom10 · Answer 2 · 2012-04-08T20:36:43.673

2

Arduino has the built-in String class, and in that you can do:

String stringOne = "A long integer: ";
// using += to add a long variable to a string:
stringOne += 123456789;

// or

stringTwo.concat(123456789);

and if both cases you get "A long integer: 123456789".

edited Apr 08 '12 at 20:36

answered Apr 08 '12 at 03:48

tom10

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score 2 · Answer 3 · answered Apr 08 '12 at 09:19

I strongly recommend to use 2 helper libraries. Those together make using strings so much easier!

PString: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1236036180 so you can write...

str.print("The temperature is ");
str.print(temp);
str.println(" degrees.");
// do something with str here

Streaming: http://arduiniana.org/libraries/streaming/ So you can write...

lcd << "GPS #" << gpsno << " date: " << day << "-" << month << "-" << year << endl;

score 0 · Answer 4 · answered Apr 10 '12 at 21:35

The equivalent of your JavaScript code as an Arduino sketch is:

void setup() {
  Serial.begin(9600);
  int c = 33;                 // var c = 33;
  String myString = "hello";  // var myString = "hello"
  myString += c;              //                        + c;
  Serial.println(myString);   // alert(myString); //---> hello33
}

void loop() {
}

For string handling, the differences between the JavaScript and the Arduino (C++) code are:

Variables are strongly typed. For example, you need to indicate if a variable is an integer (int) or a string (String) when you declare it.
Strings are not built-in 'primitive' types in C++ (and the Arduino version of C++ does not support the C++ standard library string either) so some simple manipulations cannot be performed as a single statement. For example, the assignment and concatenation requires two lines of Arduino code.

Other important differences between your JavaScript and the Arduino (C++) code are:

You need both a setup and loop function rather than a main function. setup runs only once when power is applied to the Arduino board and then loop is executed continually.
The nearest equivalent of JavaScript's alert in Arduino is to write to the serial port. To see this output you will need the Arduino board to be connected to a PC. Within the Arduino IDE, turning on the Serial Monitor will allow you to see the output.

C: string manipulations and Arduino

4 Answers4