How to Use Strings in Arduino: Syntax and Examples

In Arduino, you can use String objects to work with text easily or use character arrays (char[]) for more control. Use String for simple text handling and char[] when memory is limited or you need C-style strings.

Syntax

Arduino supports two main ways to use strings: String objects and character arrays. String is a class that lets you work with text easily, while char[] is a traditional C-style string stored as an array of characters ending with a null character '\0'.

Here is the basic syntax for both:

arduino

String myString = "Hello, Arduino!";

char myCharArray[] = "Hello, Arduino!";

Example

This example shows how to create a String, append text, and print it to the Serial Monitor.

arduino

void setup() {
  Serial.begin(9600);
  String greeting = "Hello";
  greeting += ", Arduino!";  // Add text to the string
  Serial.println(greeting);  // Prints: Hello, Arduino!
}

void loop() {
  // Nothing here
}

Output

Hello, Arduino!

Common Pitfalls

Using String objects can cause memory fragmentation on small Arduino boards with limited RAM, leading to crashes. To avoid this, use char arrays for fixed or small strings.

Also, remember that char arrays must end with a null character '\0' to mark the end of the string.

arduino

/* Wrong way: Using String in a loop can cause memory issues */
void loop() {
  String temp = "Count: ";
  temp += String(millis());  // This creates many temporary String objects
  Serial.println(temp);
  delay(1000);
}

/* Better way: Use char array and snprintf */
void loop() {
  char temp[20];
  snprintf(temp, sizeof(temp), "Count: %lu", millis());
  Serial.println(temp);
  delay(1000);
}

Quick Reference

• String: Easy to use, dynamic size, but can cause memory issues on small boards.
• char[]: Fixed size, manual management, safer for limited memory.
• Use += to add text to String objects.
• Use snprintf or strcpy for char[] manipulation.
• Always end char[] strings with '\0'.

Key Takeaways

Use String objects for easy text handling but be cautious on small memory boards.

Use char[] arrays for fixed or memory-critical string operations.

Always terminate char[] strings with a null character '\0'.

Avoid creating many temporary String objects in loops to prevent memory fragmentation.

Use += to append text to String objects and snprintf for char[] formatting.