Create a TextFile from a File Descriptor

[MMarie]

Hi,

I am working on a program which processes some text, this text can come from either STDIN or a file which's path was provided as a parameter. For the past 30 minutes ive been trying to find out how I could easily fallback to STDIN unsuccessfully. I desperatly want to avoid having to wrap every call to read in an if condition and so on, and would much prefer if i could just do something basically equivalent to this:

Code: Pascal  [Select][+][-]

1. procedure foo(filename: string);
2. var
3.   file: TextFile;
4. begin
5.   if Length(filename) = 0 then
6.     Assign(file, StdInputHandle)
7.   else
8.     Assign(file, filename);
9.  
10.   { go on and do something ... }
11. end;
12.  

Thank you in advance for your help

[MMarie]

Nevermind, I found it on "accident" whilst googling for something else, I was looking for "Input" from the System unit...

[MarkMLl]

I know that this is after the event, but as background: originally, Pascal's initial "program" statement read like

Code: Pascal  [Select][+][-]

1. program(input, output);
2.  

or sometimes

Code: Pascal  [Select][+][-]

1. program(input, output, error);
2.  

where the two or three program parameters where bound in a way specific to the operating system to external sources or sinks of line-by-line data (i.e. Pascal's "text" file type). The mapping was- in the early days- set up by control cards when the student (etc.) submitted his program to the mainframe, in unix terms they correspond to the < > and 2> redirections.

It actually makes a lot of sense: the program parameters as viewed from inside the program look like function parameters viewed from inside a function.

If you're feeling brave- very brave- the example at https://forum.lazarus.freepascal.org/index.php/topic,60666.msg454852.html#msg454852 applies: the first few lines are control cards, note the FILE OUTPUT directive.

MarkMLl

[silvercoder70]

Another way around that would be to create an abstract class (?) like TInputStreamBase and implement 2 classes from that like - TInputStream and TInputFileStream (to avoid conflict) with however you want to do read/write classes. Then ...

Code: Pascal  [Select][+][-]

1. procedure Fpo(...)
2. var
3.   stream: TInputStreamBase;
4. begin
5.   if filename = '' then
6.     stream := TInputStream.Create(...)  
7.   else
8.     stream := TInputFileStream.Create(...)
9.  

and just use stream after this.