I'm writing a sketch for a Wemos D1 Mini to display a web page. This works and I can get Unicode characters to display, but if I try to use ones with surrogate pairs like 🔊 I get a compile error;

  s += "\uD83D\uDD0A";


\uD83D is not a valid universal character

How can I get this character in my code?

  • Google the error message "\uD83D is not a valid universal character" and you fill find lots of answers.
    – user31481
    Jul 12, 2017 at 22:27

2 Answers 2


There is a nifty new feature in C++11 called string literal, this example shows how to use it with any single line or multi line or utf8 text. You just define starting and ending sequence, in following case --- (starting sequence becomes R"---( and ending sequence )---") and make sure that this sequence does not appear in encapsulated text. This is great for integrating websites into arduino projects:

static const char _index_html[] PROGMEM = R"---(
<link rel="icon" type="image/png" href="/favicon.png"/>
  • Okay, but what does that have to do with the SMP? Or anything outside ASCII for that matter? May 9, 2018 at 12:18
  • If he had used any unicode capable editor, he could just copy/paste any unicode symbols without caring how to encode them - no need to use escaping sequences. Also this answers shows how to easily integrate mutliline HTML code into arduino project
    – gabonator
    May 9, 2018 at 12:30

After some trial and error, I got it using the python style u"\U0001F50A" without the leading u of course

  s += "\U0001F50A";

Too bad I didn't think about googling the error msg, would have saved me some time.

  • 1
    Can you use pure UTF-8 characters in the source code ? It is a risk, because everything should be able to handle them. I think it should work. At least this forum can handle pure UTF-8 characters: ±10 °C, 10 µm, 1 kΩ, ¿
    – Jot
    Jul 13, 2017 at 1:03
  • Actually, you can. I didn't even try that.
    – Musa
    Jul 13, 2017 at 2:50

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