Converting uint8_t to String - unexpected result

Question

I'm working on a remote control code for ESP controller. Using ESPwebserver and Fastled. When I try to return a value of an uint8_t, as a POST response, i got strange result here is the relevant code:

uint8_t PaletteBrightness = 255; 
server.on("/Sync", HTTP_POST, []() {
String Sync = "PaletteBrightness:" + PaletteBrightness;
 Sync += ":end";
 Serial.println(Sync);
 server.send(200, "text/plain", Sync);
 });

The code complies, and runs fine but the result of 'Sync' in both serial, and POST response is:

Phase:end

Why? What does even Phase mean?
What I want is:

PaletteBrightness:255:end

Where the 255 is the value of 'uint8_t PaletteBrightness' Also, there will be more values, to add the 'Sync' string. Just trying to get one right.

Answer 1

You should convert your number uint8_t into it's ASCII representation before appending it to your string, otherwise you are appending just one character using it's byte representation.

To do so you can use a standard function itoa() which has a decent documentation available here.

So change line

 String Sync = "PaletteBrightness:" + PaletteBrightness;

into

 char buffer [4];
 String Sync = "PaletteBrightness:" + itoa(PaletteBrightness, buffer, 10);

• Nah: I've ended up using String(PaletteBrightness); And it seems to do the trick. Would it be better to use itoa()?
• Majenko: Avoid the use of String at all costs unless there absolutely no alternative. hackingmajenkoblog.wordpress.com/2016/02/04/…
• Nah: Will read this trough. I need to send and receive data from client which is done in http post, effectively plain text. Don't think there is a way around strings there.
• Roberto Lo Giacco: Yes, there is at least another way: array of chars. And before you ask, strings are not just array of chars, remember you are dealing with C here, not Java or JavaScript. Also memory is a big constraint, anything that is dynamically allocated must be strictly controlled and memory fragmentation can quickly become an issue.
• Nah: Okay, I read up on String, and now i understand a bit better why are they bad. However, ESP8266WebServer.h Uses lots of Strings, and related String object functions. Isnt that also wrong? or I'm missing some key elements here.