Arduino String Object

Arduino String Object
Arduino String Object

The Arduino String class represents a string and enables us utilize it in sketches. A string is a group of characters in double or single quotations. When storing data characters, strings are most often utilized. We use classes while using string objects. The Arduino String library’s String object is a class. String objects are dynamic and can alter in length, making it difficult to determine how many characters a file contains. Writing them to a file is more involved than writing fundamental data.

However, the String library and functions allow us to mix and match these functions to write to a file. Simply put, this manual teaches us how to define, declare, and use Arduino classes. The documentation covers class definition, instance creation, and class function calling. The main purpose is to explain class syntax and functionalities. After reading the handbook, we should be able to sketch classes, instances, and member functions. This will allow us to write more complicated code with multiple data kinds and variables. This document should give a basic introduction to Arduino classes.


A technical and syntactical definition Arduino String Object  is a series of characters that starts and ends with double quotes and includes special characters like /, \, and “. This definition sets or returns a String object’s value. This code runs when you declare a String in the sketch. Such as the following declaration: String str = “ABC”; declaration code executes, returning “ABC”. Strings are usually defined with definitions. Note that the Arduino compiler will place a definition above the main body code just before the function setup(), and each definition will be contained in its own block of pre-processor commands or ‘directives’ that start with # and use up to the end of the line.

In Arduino code, a definition is “#define identifier definition” where #define is used to define a macro, which is like a constant for the pre-processor; the identifier is the name of the definition, and if it is typed anywhere in the code, the definition’s value will be pasted in; and the definitioniropr could be a String (sequence of characters) as described above, an integer, real, or


Setting the maximum dimension of the chars array used to store strings and managing null characters to terminate strings are implemented by this class. The string length and buffer are private variables, thus a private constructor specifies the maximum string length. This prevents code from changing the char’s array string dimension. As the string can be updated, a protected function called setString assigns a value and is a class buddy. This function does what StringBuffer’s replace function does when a new string value is given: reallocate memory for the pointer to the char array and insert the string in place. The function additionally reserves ‘raw’ memory to store the string and copy the content from the original buffer String using dynamic memory allocation.

This also prevents this memory from being rewritten or utilized by another pointer object. Strcpy assigns a string to the string buffer. Every string object has the method length, which counts each byte of the string in the char’s array up to the null character like strlen. This eliminates ‘extra’ bytes and determines string length. Since the String class has a built-in length method, two methods with the same name are not allowed. However, my reading of StringBuffer class method length already distinguishes the term used here and here. The method header for this method includes the keyword virtual, int data type, method name, parenthesized parameter list, and curly braces. When the derived class String for the Arduino’s class String writes code to process text handled by its objects, the length method will be practically visited.

An Introduction to Arduino String Objects

What is a String Object?

Use the String object to modify text strings in Arduino sketches. A string is a sequence of letters, numbers, and symbols. Instead of storing characters in arrays and manipulating them separately, the String object includes built-in methods to simplify string handling.

Making String Objects
You can construct String objects several ways. The simplest is: This generates a String object called myString with the value “Hello”.

Create and add empty strings:

emptyString += “Hello”; // “Hello”
// emptyString += “World!”Now String is “Hello World!”

Methods with strings
The String object contains several helpful methods. Some common ones are:

length() returns string length.

upperCase() – Uppercases the text

lowercase() lowercases the text

substring() – Extracts a string substring

replace() swaps substrings.

IndexOf() finds the first substring index.

This function retrieves the character at an index.

As an example:

length = greeting.length(); // 5
Upper = hello.upperCase(); // “HELLO”
Greeting string sub.Substring(1, 3); // “el”

Concatenating Strings

Use the + operator to concatenate String objects:

String second = “World”; String combined = first + ” ” + second; // “Hello World”

Use String objects in Arduino programs to simplify string operations. Enjoy playing with String object methods and creating fascinating projects!

Creating, Concatenating, and Modifying Strings

After learning about Arduino strings, create, combine, and manipulate them.

Creating Strings

A string can be created: MyString = “Hello”;

This produces a “Hello” String object called myString.

Concatenating Strings

The + operation concatenates strings: FirstName = “John”; LastName = “Doe”; String fullName = firstName + lastName; // “John Doe”

Modifying Strings

  • A string can be modified in many ways:
  • Get myString.length().
  • Get a character at index: myString[0].
  • Replacement: myString.replace(“Hello”, “Hi”).
  • Uppercase myString.toUpperCase()
  • Lowercase myString.toLowerCase()
  • Trim whitespace: myString.trim()
  • And more! Many string methods are useful.

Learning string manipulation with Arduino brings up new options. Combining and manipulating strings generates dynamic messages, parses sensor information, creates web requests, and more. Try it and enjoy it! String has several capabilities.

Nice String Methods for Code

After working with Arduino’s String object, you’ll find numerous useful string manipulation techniques. These are the most popular drawing elements.

Use.length() to get a string’s character length. As an example:

theString’s length is 5

toUpperCase(), toLowerCase()
These techniques transform strings to uppercase or lowercase. As an example:

UpperCase = myString.toUpperCase(); // “HELLO”
String lowerCase = myString.toLowerCase(); // “hello”

Use.substring() to extract string fragments. Pass it a start and end index to get the substring between them. As an example:

Substring = myString.substring(0, 5) = “Hello”

Replace all instances of a character (or substring) in a string with another using the.replace() method. As an example:

// “Hellx Wxrld” is the new string created by replacing “o” with “x” in myString.

indexOf(), lastIndexOf()
These techniques find the first/last character/substring in a string. They return the match index or -1 if no match is found. As an example:

Int firstO = myString.indexOf(“o”); // firstO = 4 // lastO = 7

These methods let you modify strings in Arduino projects in different ways. Have more questions? Let me know!

Flash Memory and String Storage

As Arduino projects become more complicated, you’ll need to save longer strings for LCD panels or serial connection. For longer strings, use the Arduino’s flash memory because its 2KB of SRAM fills very quickly.

Declaring Flash Strings
F() macros declare flash memory strings. As an example:

str1[] = “Hello”; // SRAM entry
[char str2] “World”; // Flash memory

String str1 uses 5 bytes of SRAM, while str2 uses flash.

Read Flash Strings
Reading flash strings requires the F() macro again. As an example:

Printing “Hello” and “World” with Serial.println(str1) and F(str2), respectively.

The F() macro instructs the compiler to read the string from flash instead of SRAM.

Saving SRAM

String storage in flash saves hundreds of SRAM bytes. SRAM requires 100 bytes to hold a 100-character string, while flash only needs 2 bytes for the pointer.

Flash strings have some restrictions:

Runtime flash string changes aren’t possible. They must be compile-time declared.

Use the F() macro to embed flash strings in code. SD card and serial strings can’t be read into flash.

Memory alignment can make flash strings 3 bytes per character instead of 1. Flash may not be memory-efficient for short strings.

Reading or writing flash strings requires the F() macro. Simply accessing str2 reads SRAM, not flash!

You can construct more complex Arduino projects that store more string data by knowing how to declare, read, and access flash strings. Flash strings are useful Arduino programming tools!

Limitations and Alternatives for String Objects

Sizing Limit

Arduino String objects are limited to 2,048 bytes. Arduino boards have limited memory, with the Uno having 2 KB SRAM and 32 KB flash. Unexpected errors can occur after exceeding the size limit.

First option: PROGMEM

Use PROGMEM to store strings in flash memory to avoid this constraint. The Uno will have 32 KB more room because your string will be in program memory instead of SRAM. Declaration of PROGMEM string: const char string[] “Your string here”;

Use char buffer[20]; strcpy_P(buffer, string); to access this string. Copy PROGMEM to your buffer array.

Option 2: External EEPROM

An external I2C EEPROM chip can store strings larger than 32 KB. The Microchip 24LC256 EEPROM holds 256 KB, sufficient of room for strings and other data. Write strings to EEPROM with EEPROM.write().

Read strings from EEPROM is more complicated since you must track the memory addresses where each string begins and finishes. With proper bookkeeping, an EEPROM can store vast amounts of string data for your Arduino project.

Option 3: SD Card

The SD library can store strings on SD cards for big storage demands. A 32 GB SD card has plenty of room for strings, photos, audio files, and other project materials. Arduino SD card reading and writing requires higher coding complexity. SD cards offer more space and flexibility, which may be worth the extra effort for some applications.

Overall, don’t let the String object slow down your Arduino project. PROGMEM, EEPROM, and SD cards let you expand string storage and construct more complex Arduino apps.


That concludes Arduino string basics. String allows text manipulation like concatenation, comparison, and number conversion. Remember those memory consumption and copy constructor gotchas. Practice makes string handling second nature. Start stringing Arduino projects stylishly now. Mastering Arduino strings opens up unlimited coding opportunities!

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