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I'm using an ESP32 connected to an external memory flash where I mounted a FATFS partition.
I don't understand what could happen if I turn off the ESP32 (and the flash) after a fopen() instruction. The main purpose is to avoid any corruption of the file being read or written.
In particular I use a rb+ argument for the fopen() when I read the file, and a wb when I write on it.

In which case I can obtain errors on the opened file, if something such as an unwanted switch off of the system happens?

Filippo
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  • Check the values returned by the file handling functions. `fopen()`, `fread()`, `fwrite()` and `fclose()` all tell you what happened. – Weather Vane Jun 29 '22 at 12:57
  • @WeatherVane you mean that if they all give a correct value then the file is still valid, correct? – Filippo Jun 29 '22 at 13:43
  • After writing to a file, you can read the file back and compare with the original to check if it is correct. – Weather Vane Jun 29 '22 at 14:16
  • @WeatherVane hence I think you are saying that there isn't a standard behavior, it must be experimented. – Filippo Jun 29 '22 at 14:27
  • You asked what you can do to verify that the file is correct, when all the file functions have returned the correct values. The way to do that is to read the file, but (in general) there is no guarantee that the file is correct even then, and isn't sitting in a cache. Of course you must experiment: that is what testing is all about. Interrupt the process and see if the software behaves correctly. What we seek is a level of confidence. There are never 100% guarantees, ever. For example there might be a glitch that makes your checking software report 'true' when it is 'false', or vice-versa. – Weather Vane Jun 29 '22 at 14:30
  • I noticed that turning off the system during a read operation (in particular after the `fread()` but before the `fclose()`) I didn't noticed problems in the values returned by `fopen()`, `fclose()` and `fread()`. – Filippo Jul 04 '22 at 07:19
  • If you turned it off after `fread()` was successful why was there a problem? Was the data incorrect? – Weather Vane Jul 04 '22 at 07:23
  • Data seems to be not corrupted after this kind of operation. In the case of `fwrite()` operation the problem shouldn't exist in my case because I check the size of the file and, if it doesn't coincides with a pre-determined one, the file is deleted. However I'm not 100% peaceful with this topic, if I'll have an opportunity, I'll dig more in depth! – Filippo Jul 04 '22 at 10:52

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