The aim is to display a non-static html page depending on some variable condition.

The code I created hast the problem, that the esp8266 is ressetting in the moment I request the page.

const char htmlIndexHeader[] PROGMEM = R"=====(
    <meta http-equiv="content-type" content="text/html;charset=UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1">
  <p>Hello World</p>

const char htmlIndexProgress1[] PROGMEM = R"=====(

const char htmlIndexProgress2[] PROGMEM = R"=====(

const char htmlIndexFooter[] PROGMEM = R"=====(

char htmlIndexAll[2000]; 

void handleRoot() 
  Serial.println("GET /");

   strcpy(htmlIndexAll, htmlIndexHeader);

     strcat(htmlIndexAll, htmlIndexProgress1);

     strcat(htmlIndexAll, htmlIndexProgress2);

   strcat(htmlIndexAll, htmlIndexFooter);

  server.send(200, "text/html", htmlIndexAll);

If I display a static page the esp8266 does not restart at page request.

  • 2
    try strcpy_P and strcat_P
    – Juraj
    Dec 14 '19 at 14:15
  • 1
    @Juraj it is working!
    – kimliv
    Dec 14 '19 at 18:27

Compiler can't differentiate the PROGMEM strings from constant strings in SRAM strings. Both are const char*. But the PROGMEM string must be handled differently. For that reason _P variants of functions exists.

You should use stcpy_P and strcat_P functions.

Note: On esp8266 some functions of Arduino core use a trick to identify PROGMEM strings by their specific address range.

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