Constructs an instance of the String class. There are multiple versions that construct Strings from different data types (i.e. format them as sequences of characters), including:

  • a constant string of characters, in double quotes (i.e. a char array)
  • a single constant character, in single quotes
  • another instance of the String object
  • a constant integer or long integer
  • a constant integer or long integer, using a specified base
  • an integer or long integer variable
  • an integer or long integer variable, using a specified base
  • a float or double, using a specified decimal places

Constructing a String from a number results in a string that contains the ASCII representation of that number:

  • The default is base ten, so: String thisString = String(13); gives you the String "13".
  • However, you can use other bases. For example: String thisString = String(13, HEX); gives you the String "D", which is the hexadecimal representation of the decimal value 13.
  • Or if you prefer binary, String thisString = String(13, BIN); gives you the String "1101", which is the binary representation of 13.


String(val) String(val, base) String(val, decimalPlaces)


  • val: a variable to format as a String - 허용되는 자료형: string, char, byte, int, long, unsigned int, unsigned long, float, double
  • base (optional): the base in which to format an integral value
  • decimalPlaces (val 이 float 또는 double): the desired decimal places


  • an instance of the String class.

예제 코드

All of the following are valid declarations for Strings.

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 String stringOne = String(5.698, 3); // using a float and the decimal places


※ 주의 및 경고:

If the string is modified, it is highly recommended using String.reserve() to prevent the memory fragmentation issue



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