How to Convert String to Char in Arduino

Ammar Ali Feb 02, 2024
  1. Introduction to the toCharArray() Function
  2. Convert String to char Using the toCharArray() Function in Arduino
  3. Convert Data to char Using the toCharArray() Function and the Append Operator in Arduino
  4. Practical Examples
  5. Conclusion
How to Convert String to Char in Arduino

This tutorial will discuss a method to convert a string into char - the toCharArray() function. It will also introduce how to convert other data types into char using the toCharArray() function and append operator.

Introduction to the toCharArray() Function

In Arduino programming, a String is a flexible data type used to store character sequences. However, there are situations where you need to work with char arrays, particularly when interacting with libraries or APIs that expect character arrays as inputs. This is where the toCharArray() function comes to the rescue.

The toCharArray() function allows you to convert the contents of a String object into a char array. It provides a seamless way to bridge the gap between these two data types.

Syntax of the toCharArray() Function

The syntax of the toCharArray() function is straightforward:

stringObject.toCharArray(charArray, length);
  • stringObject: The String object you want to convert.
  • charArray: The target char array to store the converted characters.
  • length: The length of the String object plus one for the null terminator.

Convert String to char Using the toCharArray() Function in Arduino

This method copies the string’s characters to the supplied buffer. It requires two inputs, one is a buffer to copy the characters into, and the other is the buffer size.

void loop() {
  String stringOne = "A string";
  char Buf[50];
  stringOne.toCharArray(Buf, 50);

In the above code, stringOne is the String object where the string is stored. Buf is the char array where the result is going to be saved. In this example, we use a buffer length of 50, but you can change that according to the given string. Check the link for more details.

Convert Data to char Using the toCharArray() Function and the Append Operator in Arduino

If you want to convert any other data type instead of String, you can use it. First of all, you need to convert the other data type into String using the append operator; then, you can use the above method to convert this String into char.

void loop() {
  String stringOne = "A long integer: ";
  stringOne += 1234;
  char charBuf[50];
  stringOne.toCharArray(charBuf, 50);

In the above code, we have an integer - 1234 and add it to an existing String using the append operator to convert them into a char array. Check this link for more information.

Practical Examples

Let’s explore a couple of practical examples to solidify your understanding.

Example 1: Sending Data over Serial

Suppose you want to send sensor readings over the serial port as a char array. Here’s how you can do it:

void loop() {
  int sensorValue = analogRead(A0);
  String dataToSend = "Sensor reading: ";

  // Append the sensor value to the String
  dataToSend += sensorValue;

  char charArray[dataToSend.length() + 1];  // +1 for the null terminator

  dataToSend.toCharArray(charArray, dataToSend.length() + 1);

  Serial.println(charArray);  // Send the data over serial

Example 2: Displaying on an LCD Screen

Imagine you want to display a dynamic message on an LCD screen. Here’s how:

#include "LiquidCrystal.h"

LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

void setup() { lcd.begin(16, 2); }

void loop() {
  int sensorValue = analogRead(A1);
  String message = "Sensor value: ";

  // Append the sensor value to the String
  message += sensorValue;

  char charArray[message.length() + 1];  // +1 for the null terminator

  message.toCharArray(charArray, message.length() + 1);

  lcd.print(charArray);  // Display the message on the LCD screen


Mastering the toCharArray() function in Arduino empowers you to seamlessly convert String objects to char arrays and work with them effectively.

Whether you’re sending data over serial communication, displaying messages on an LCD screen, or interacting with external libraries, the ability to perform this conversion is a crucial skill.

By following the guidelines and practical examples in this guide, you’re now equipped to handle such scenarios with confidence.

Author: Ammar Ali
Ammar Ali avatar Ammar Ali avatar

Hello! I am Ammar Ali, a programmer here to learn from experience, people, and docs, and create interesting and useful programming content. I mostly create content about Python, Matlab, and Microcontrollers like Arduino and PIC.

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