ESP32 Forum

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struct SDATA {
  float temp;
  long  tmillis;
};

SDATA TabMesures[3600];

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http_server.on(HTTP_GET, "/data.csv") {
    response.header.set("Content-Type", "text/csv");
    // TODO: set Content-Length or use chunked encoding
    response.begin();
    for(int row = 0; row < ARRAY_SIZE(TabMesures); ++row) {
        char buffer[20];
        sprintf(buffer, "%.2f", TabMesures[row].temp);
        response.send(buffer);
        response.send(',');
        sprintf(buffer, "%ld", TabMesures[row].tmillis);
        response.send(buffer);
        response.send('\n');
    }
    response.end();
}

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sprintf(buffer, "%.2f",...) 

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dtostrf()

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#define NUMVALUES 3600
#define CHARSPERVALUE 36
static char tabvals_csv[NUMVALUES * CHARSPERVALUE] = "";

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void fillTabMesures(){
  int n;
  char tabvalue[CHARSPERVALUE] = "";
  for (int i=0;i<(NUMVALUES);i++){
    float value = float(i)/100.0;
    unsigned long  tnow = millis();
    n = sprintf(tabvalue,"%7.2f,%22lu,\n", value, tnow);
    strcat(tabvals_csv,tabvalue);
  }
}

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    server.on("/tabvals.csv",handletabvals);

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void handletabvals(){
    server.send(200, "text/csv", tabvals_csv);
}

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   0.00,                   793,
   0.01,                   793,
   0.02,                   793,
   0.03,                   793,
   0.04,                   793,