Reading a file without while() loop

Using Arduino Programming Questions
1

hello !

My question is really simple. I'd like to know if it's possible to read a file from my SD Card on my ethernet shield without using a while loop.
I'm currently using this code :

fh = SD.open(filename);

if(fh)
{
      while(fh.available())
      {
         Serial.println(fh.readStringUntil('\n'));
      }
      fh.close();
}
else
{
       Serial.println("Error opening the file");
}

As you can see, using this method will "block" my sketch, and I won't be able to perform any actions beside reading the file.
Is there a way to allow me to read my file and still perform actions (such as blinking a led) ?

Thanks for your help!

2

Yes. Change to if() to only read one character at a time. Then you will need a further if() so that you only open the file once instead of opening it on every pass through the loop. Or put the file open into setup().

3

MorganS:
Yes. Change to if() to only read one character at a time. Then you will need a further if() so that you only open the file once instead of opening it on every pass through the loop. Or put the file open into setup().

I need to open my file at differents times during my sketch. So i can't open it in my setup().

1- I'm writing data into the file when I'm logging a RFID Tag.
2- I'm reading file to send the content through my ethernet shield. (this is why I need to read my file and still be able to perform actions).

I already tried to use a if() and it's only reading the first line of my file. :confused:

4

Use a flag to determine if the file is open.

boolean sdOpen = false;

if(!sdOpen) {
  // open the file
  sdOpen = true;
}

if(sdOpen) {
  // read/write file
}
5 
loop(){
  static boolean FileIsOpen = false;

  if(FileIsOpen) {
    if(fh.available()){
         Serial.println(fh.readStringUntil('\n'));
    } else {
      fh.close();
      FileIsOpen = false;
  } else {
    if(weNeedToSendEthernetNow()) {
      fh = SD.open(filename);
      FileIsOpen = true;
    }
  }
}
6

MorganS:

loop(){

static boolean FileIsOpen = false;

if(FileIsOpen) {
    if(fh.available()){
        Serial.println(fh.readStringUntil('\n'));
    } else {
      fh.close();
      FileIsOpen = false;
  } else {
    if(weNeedToSendEthernetNow()) {
      fh = SD.open(filename);
      FileIsOpen = true;
    }
  }
}




Isn't the fh.available() going to loop only once ? So it will always return the first line of my file.

Thanks for your support guys. I really appreciate it.
7

No, it won't go back to the start of the file because it doesn't reopen the file if it's already open.

You haven't posted enough of your code. Is fh a local or global variable?

8

MorganS:
No, it won't go back to the start of the file because it doesn't reopen the file if it's already open.

You haven't posted enough of your code. Is fh a local or global variable?

It's a global ! But from what I've tested from now, everything seems to be working fine thanks to you !

Thanks a lot! :smiley: