$ftell(file descriptor)

This function returns the current position of the file pointer, measured in bytes from the beginning of the file. This value can be used to save your position in the file, and you can later use

  $fseek(//file descriptor// SET //ftell-value//)

to resume your place.

The file descriptor must have been a value previously returned by the open function.

-1   Error: //file descriptor// was not previously returned by [[open]], or //anchor// is not supported.