Working with an array of type TextFile

[Wilko500]

MacOS LazFPC 40RC2/323

The program re-write I am working on requires that I log inverter data every 1 minute to text files. There are 16 log files.  The inverter data that is being read will be stored in a record or array.  It seems that from an efficiency point of view a good approach is to open all the files at start of program and leave them open thus avoiding resource expensive open/close operations.

While considering how to program this other than a list of statements for open, update and then close it occurred to me that I am dealing with 16 identical processes so why not place them in arrays.  The following code snippet shows what I have tried.  While I did not expect it to work it does but I don't understand why. The line that puzzles me is

Code: Pascal  [Select][+][-]

1.   arFile: Array[1..3] Of TextFile;  

because I don't initialise the contents of arFile thus I would have expected that each element is null but I do end up with multiple files being created as desired.

Have I been lucky that my code snippet works?  Is there a better/safer way to code this task?

Code: Pascal  [Select][+][-]

1. Var
2.   i:   Int32;
3.   num: Single;
4.   arFile: Array[1..3] Of TextFile;
5.   arFileName: Array[1..3] Of String;
6.  
7. Begin
8.    for i:= 1 to 3 do
9.        begin
10.        arFileName[i]:= g.DebugLogFilePath + '/File' + IntToStr(i) + '.cht';
11.        assignFile(arFile[i],arFileName[i]);
12.        ReWrite(arFile[i]);
13.        end;
14.  
15. For i:= 1 to 3 do
16.     Begin
17.     writeln(arFile[i], 'Hello textfile!');
18.     writeln(arFile[i], 'Hello textfile Line two');
19.     CloseFile(arFile[i]);
20.     end;  

[dseligo]

because I don't initialise the contents of arFile thus I would have expected that each element is null but I do end up with multiple files being created as desired.

arFile[ i ] is being initialized with assignFile (which is same as System.Assign) - in line 11 of your example.

[Wilko500]

Thanks for that clarification.  I looked up System.Assign which I didn't know was a thing   Makes sense now. While I have used AssignFile in its simplest context many times I never really considered what it was doing. I see now that my arFile element is no different to a single Var. 

Code: Pascal  [Select][+][-]

1. Assign assigns a name to F, which can be any file type. This call doesnt open the file, it just assigns a name to a file variable, and marks the file as closed
2. Note that the filename (including path) can be only 255 characters long.

[dseligo]

I see now that my arFile element is no different to a single Var.

Exactly.