ESPFlash: Open a file with a filename of “/lengthExample” and get the number of elements stored in the file with error checking.

ESPFlash_example3.cpp

/*
Open a file with a filename of “/lengthExample” and get the number of 
elements stored in the file with error checking.
*/
ESPFlash<double> lengthExample("/lengthExample");
uint32_t numberOfElements = lengthExample.length();

/* The above code replaces the following SPIFFS implementation */
File file;
uint32_t sizeInBytes = 0;
uint32_t sizeInElements = 0;
SPIFFS.begin();  
file = SPIFFS.open("/lengthExample", "r");
if(file)
{      
  sizeInBytes = file.size();
  sizeInElements = sizeInBytes/sizeof(double);
}
file.close();