Arduino:
Extracting substrings

How to:

Arduino strings can be sliced and diced using substring():

void setup() {
  Serial.begin(9600);
  String phrase = "Hello, Arduino World!";
  String greeting = phrase.substring(0, 5);
  String location = phrase.substring(7, 19);
  
  Serial.println(greeting); // Prints "Hello"
  Serial.println(location); // Prints "Arduino World"
}

void loop() {
  // Nothing to loop over here.
}

Output on Serial Monitor:

Hello
Arduino World

Deep Dive

Way before Arduino made it simple, programmers used char arrays and functions like strncpy in C. Not just historical relics, they’re still in use for lower-level operations. The substring() function in Arduino is actually a wrapper that makes it easier for us when dealing with String objects. But be aware, using String can lead to memory fragmentation. If stability’s crucial, especially in long-running or complex programs, consider the old ways of char arrays.

Alternatives to substring() include direct char array manipulation or functions like strtok(). These can be more efficient but might leave you with more code to manage.

Under the hood, substring() creates a new String object containing the characters from the starting index to just before the ending index, which can be omitted if you want everything till the end.

See Also:

• Arduino String Reference: https://www.arduino.cc/reference/en/language/variables/data-types/stringobject/
• Memory Management in Arduino: https://learn.arduino.cc/programming/variables-and-data-types/memory-management
• C++ std::string substr method, for comparison: http://www.cplusplus.com/reference/string/string/substr/