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String Object Constructors

The String object allows you to manipulate strings of text in a variety of useful ways. You can append characters to Strings, combine Strings through concatenation, get the length of a String, search and replace substrings, and more. This tutorial shows you how to initialize String objects.

String stringOne = "Hello String";                  // using a constant String
String stringOne =  String('a');                    // converting a constant char into a String
String stringTwo =  String("This is a string");    // converting a constant string into a String object
String stringOne =  String(stringTwo + " with more");// concatenating two strings
String stringOne =  String(13);                     // using a constant integer
String stringOne =  String(analogRead(0), DEC);     // using an int and a base
String stringOne =  String(45, HEX);                // using an int and a base (hexadecimal)
String stringOne =  String(255, BIN);               // using an int and a base (binary)
String stringOne =  String(millis(), DEC);          // using a long and a base

All of these methods are valid ways to declare a String object. They all result in an object containing a string of characters that can be manipulated using any of the String methods. To see them in action, upload the code below onto an Arduino and open the Serial Monitor. You'll see the results of each declaration. Compare what's printed by each println() to the declaration above it.

Hardware Required

  • Arduino Board

Circuit

There is no circuit for this example, though your Arduino must be connected to your computer via USB.

image developed using Fritzing. For more circuit examples, see the Fritzing project page

Code

/*
   String constructors
 
 Examples of how  to create strings from other data types
 
 created 27 July 2010
 modified 30 Aug 2011
 by Tom Igoe
 
 http://arduino.cc/en/Tutorial/StringConstructors
 
 This example code is in the public domain.
 */


void setup() {
  // Open serial communications and wait for port to open:
  Serial.begin(9600);
  while (!Serial) {
    ; // wait for serial port to connect. Needed for Leonardo only
  }
 
  // send an intro:
  Serial.println("\n\nString Constructors:");
  Serial.println();
}

void loop() {
  // using a constant String:
  String stringOne = "Hello String";    
  Serial.println(stringOne);      // prints "Hello String"

  // converting a constant char into a String:
  stringOne =  String('a');        
  Serial.println(stringOne);       // prints "a"

  // converting a constant string into a String object:
  String stringTwo =  String("This is a string");  
  Serial.println(stringTwo);      // prints "This is a string"

  // concatenating two strings:
  stringOne =  String(stringTwo + " with more");
  // prints "This is a string with more":
  Serial.println(stringOne);      

  // using a constant integer:
  stringOne =  String(13);        
  Serial.println(stringOne);      // prints "13"

  // using an int and a base:
  stringOne =  String(analogRead(A0), DEC);  
  // prints "453" or whatever the value of analogRead(A0) is
  Serial.println(stringOne);      

  // using an int and a base (hexadecimal):
  stringOne =  String(45, HEX);  
  // prints "2d", which is the hexadecimal version of decimal 45:
  Serial.println(stringOne);      

  // using an int and a base (binary)
  stringOne =  String(255, BIN);  
  // prints "11111111" which is the binary value of 255
  Serial.println(stringOne);      

  // using a long and a base:
  stringOne =  String(millis(), DEC);
  // prints "123456" or whatever the value of millis() is:
  Serial.println(stringOne);      

  // do nothing while true:
  while(true);

}

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