Interpolating a string

How to:

Arduino doesn’t have built-in string interpolation, but you can get similar results with sprintf() or by concatenating strings and variables.

char buffer[50]; // Make sure this is large enough to hold the final string
int sensorValue = analogRead(A0);
sprintf(buffer, "Sensor reading: %d", sensorValue);


Sensor reading: 402

Or using string concatenation:

String message = "Sensor reading: " + String(sensorValue);

Deep Dive

C and C++ (the core languages of Arduino sketches) traditionally don’t have string interpolation like newer languages (e.g., Python or JavaScript). Instead, sprintf() has been the go-to way to compose strings with variables. It works, but it can be a bit clunky and error-prone due to buffer overflows if not managed carefully.

Concatenation using the String class is more intuitive and safer from memory errors. The drawback? It can lead to memory fragmentation, especially in long-running programs on memory-constrained devices like Arduinos.

An alternative found in some newer or more specialized C++ libraries (not standard in Arduino) is to use string formatting libraries that provide a syntax closer to interpolation, such as fmtlib.

As for implementation details, when you concatenate with the String class, behind the scenes, the Arduino is creating new string objects and handling the memory for you. sprintf(), on the other hand, writes formatted text to a buffer you allocate, giving you more control at the cost of having to manage memory manually.

See Also