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String replace Function

The String replace() function allows you to replace all instances of a given character with another character. You can also use replace to replace substrings of a string with a different substring.

Hardware Required

  • Arduino Board


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


Caution: If you try to replace a substring that's more than the whole string itself, nothing will be replaced. For example:

String stringOne = "<html><head><body>";
  String stringTwo = stringOne.replace("<html><head></head><body></body></html>", "Blah");

In this case, the code will compile, but stringOne will remain unchanged, since the replacement substring is more than the String itself.

  String replace()
 Examples of how to replace characters or substrings of a string
 created 27 July 2010
 by Tom Igoe
 This example code is in the public domain.

void setup() {
  Serial.println("\n\nString  replace:");

void loop() {
  String stringOne = "<html><head><body>";
  // replace() changes all instances of one substring with another:
  String stringTwo = stringOne.replace("<", "</");

  // you can also use replace() on single characters:
  String normalString = "bookkeeper";
  Serial.println("normal: " + normalString);
  String leetString = normalString.replace('o', '0');
  leetString = leetString.replace('e', '3');
  Serial.println("l33tspeak: " + leetString);

  // do nothing while true:

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