ESP8266 Community Forum

- Thu Sep 17, 2015 11:33 am #29263 Hi,
talking about String-objects:
crashing without serial output.
Try this:

Code: Select allconst String html_page2 PROGMEM = "Teststring";

void setup() {
}

void loop() {
}

Crashing on my ESP-12E

my ESP8266: ESP-01 V2 / ESP-12E (NodeMCU)
ESP8266 Arduino add-on
Arduino IDE 1.6.5

- Thu Sep 17, 2015 11:36 am #29264 Same things apply here.
String class isn't PROGMEM aware, so it will try to do a memcpy() instead of memcpy_P(), this is why the crash occurs ...

- Fri Sep 18, 2015 1:53 am #29315

Code: Select allconst String html_page2 PROGMEM = "Teststring";

Actually this won't work for a more basic reason — you try to place a non-POD type into read-only memory. String class is initialized by its constructor, so when constructor tries to copy "Teststring" into the string, it causes an exception, because this String instance is in read-only memory segment.
You should use PROGMEM only for POD types or arrays of POD types.

- Sun Sep 20, 2015 3:18 am #29485 OK,
nerver heard about POD. But I am no C/C++ expert. Far away from this
But I think you wanted me to say, that I only can put Char-arrays in PROGMEM and not String-objects.
Is this only on ESP or is this causing problems on a "normal UNO" too?

For me, I will then go the way to use String-objects without PROGMEM for my HTML-Page. Two reasons:
- enough SRAM on the ESP
- can use replace() to insert e.g. actual-values into my HTML-code before sending over WiFi.

my ESP8266: ESP-01 V2 / ESP-12E (NodeMCU)
ESP8266 Arduino add-on
Arduino IDE 1.6.5