Replacing readln and writeln in a Windowed App.

[FrankThynne]

Are there standard ways of replacing the functionality of textfiles which work in console apps but not windowed apps? It's readln that I'd rather not re-implement!

 

[mikeEd]

Using Readln to read from textfiles isn't console specific; you can use it in windowed apps.

 

[sggaunt]

In fact you might want to in some situations.
You could try to use the loadfromfile method of certain componets/controls, TStrings, TStringList, but this may introduce a lot of unnessacary overhead.
Steve

 

[FrankThynne]

MikeEd: I quote from the Object Pascal reference manual:
Note: Text-oriented I/O is available only in console applications—that is, applications compiled with the “Generate console application” option checked on the Linker page of the Project Options dialog box or with the -cc command-line compiler option. In a GUI (non-console) application, any attempt to read or write using Input or Output will produce an I/O error.

I inadvertantly tried writeln(File, var, ...) after moving from a console app to a GUI app and had I/O errors - and then saw the above warning in the manual. It's possible that I was trying to use the implied Output file (and it makes sense that you can't use Input or Output in a GUI app) but the manual in unequivocal in its warning about text-oriented I/O in general.

sggaunt: Thanks but, as you suspect, I don't want the overhead of loading the whole file at once.

I've since written a crude routine to emulate readln, but still wonder if I had to bother!

 

[mikeEd]

Well, as you say, reading from/writing to standard output obviously won't work but, trust me, text oriented file IO works fine. Provided you've correctly opened the file for writing that shouldn't cause a problem.

 

[sggaunt]

Mike is right
However I belive there is a mistake in the help files relating to this that might be throwing you off (Honest).
but I cant find it today!! I seem to remember it is a Wrong file variable type assignment.

I have code based on the readln help example that works fine. The file variable here assigned as
var F: TextFile;

Steve

 

[FrankThynne]

Thanks Mike and Steve. I'm sure you're right. It makes no sense for readln and writeln to fail with disk files - and a lot of sense for Input and Output not to work in a GUI application. I suspect that the manual writer made an incorrect inference from the latter. I should have looked at my failed code (now erased) more closely - there must have been another error that misled me.

 

[mikeEd]

No, I think the manual is just referring to standard input/output and not text IO in general.