Any way to intercept stdout/stderr?

[rishav]

Hi

I want to intercept all the run time errors Pascal code may have, so that I can reformat some of them.
I don't want to wrap all Pascal code in try catches, instead I was wondering if I can provide a custom stdout/stderr interface to it, so that i can update the strigs on the fly.

Would anyone know how to go about this?

[dbannon]

rishav, I suspect most (all?) of the Pascal errors you are thinking about will terminate your application unless you handle them with a try statement.

But, maybe you are seeing some OS errors ?  The fact you know about stdout and stderr indicates you may be a linux user. GTK2, in particular generates lots of, mostly, insignificant errors. Usually distribution/desktop dependent. Damm nuisance but not much can be done about them.

Davo

[howardpc]

One possibility may be to do a search for "textfile device driver" on this or a Delphi forum, which miight allow you to redirect output text data for further processing or analysis.

[BobDog]

Windows.
This should redirect sdtdout/stderr to the console.(function console)
Everything else in the code is for a demo.

Code: Pascal  [Select][+][-]

1.  
2. uses sysutils;
3.  
4. function  system(s:pchar):integer ; cdecl external 'msvcrt.dll' name 'system';
5.  function filelength(filename:ansistring):longword;
6. Var F : File Of byte;
7. var L:longword;
8. begin
9. Assign (F,filename);
10.   Reset (F);
11.   L:=FileSize(F);
12.   Close (F);
13.   exit(L);
14. end;
15.  
16.  
17.  function loadfile(filename:ansistring):ansistring;
18.    Var Fin : File;
19.    Var x:longint;
20.    var content:ansistring='';
21.    begin
22.    x:=filelength(filename);
23.    setlength(content,x);
24.    Assign (Fin,filename);
25.    Reset (Fin,x);
26.    BlockRead (Fin,content[1],1);
27.    close(fin);
28.    exit(content);
29. end;
30.  
31.  procedure savefile(s:ansistring ;filename:ansistring);
32.     var
33.     fout:file;
34.     begin
35.     Assign(fout,filename);
36.     Rewrite(fout,length(s));
37.     blockwrite(fout,s[1],1);
38.     close(fout);
39.   end;
40.  
41.  function console(cmd:ansiString):ansistring;
42.  var
43.  _file:string;
44.  e:integer;
45.  txt:ansistring='';
46.  begin
47.  _file:=getcurrentdir+'/'+'testcode';
48.     e:=system(pchar(cmd+' '+' >>'+_file+' 2>&1'));
49.      if (e=-1) then exit('error');
50.     txt:=loadfile(_file);
51.     if fileexists(_File) then deletefile( _File);
52.     exit( txt);
53. End;
54.  
55.  
56.  
57. var
58. code:ansistring;
59. pas:ansistring;
60.  
61.  
62.  
63. begin
64. pas:=getcurrentdir+'\heloo.pas';
65.  
66. code:='var p:pinteger;'+chr(10);
67. code:=code +'begin'+chr(10);
68. code:=code+'writeln(p^);'+chr(10);
69. code:=code+'readln;'+chr(10);
70. code:=code+'end.';
71.  
72.  
73. savefile(code,pas);
74. writeln(loadfile(pas));
75. writeln(fileexists(pas));
76. writeln;
77. writeln;
78.  
79. writeln(console('fpc -vwnhi '+ pas));
80. writeln(console(getcurrentdir+'\heloo.exe'));
81. //deletefile(pas);
82. writeln('Press return to end . . .');
83. readln;
84. end.
85.  
86.  

please delete the files created by this manually.

[rishav]

Thanks everyone. I was trying to see if I can do better error reporting/formatting than what is currently possible in Free Pascal. I was hoping that it would be easier to intercept error messages than putting everything in a large try catch.

[TRon]

I was hoping that it would be easier to intercept error messages than putting everything in a large try catch.

The developer is responsible for handling errors so in those cases it does output something it is your own fault 

But since you changed the requirement to handling unhandled  exceptions:

Code: Pascal  [Select][+][-]

1. program catchyrhymes;
2.  
3. {$mode objfpc}{$H+}
4.  
5. uses
6.   sysutils, classes;
7.  
8. var
9.   rhymes: TStringList = nil;
10.  
11. procedure CatchNonHandledExceptions(Obj : TObject; Addr: CodePointer; FrameCount: Longint; Frames: PCodePointer);
12. begin
13.   rhymes.Add('You have stumbled upon an unhandled exception');
14. end;
15.  
16. procedure FamousLastWords;
17. begin
18.   if assigned(rhymes) then
19.   begin
20.     if rhymes.Count > 0 then
21.     begin
22.       writeln('---');
23.       writeln(rhymes.Text);
24.       writeln('---')
25.     end;
26.     FreeAndNil(rhymes)
27.   end;
28. end;
29.  
30. procedure SmartCalculation;
31. var x,y:integer;
32. begin
33.   y:= 0;
34.   x:= 1 div y
35. end;
36.  
37. begin
38.   rhymes:= TStringList.Create;
39.  
40.   System.AddExitProc(@FamousLastWords);
41.   System.ExceptProc:= @CatchNonHandledExceptions;
42.  
43.   writeln('To calculate');
44.   SmartCalculation;
45.   writeln('or not to calculate')
46. end.
47.  

[BobDog]

I don't use Lazarus ide, but Geany ide will keep the console open after a crash.

In windows the command to run the .exe is
'cmd /c '+ file.exe  +'& pause'
Example:

Code: Pascal  [Select][+][-]

1.  
2.  
3.  
4. uses sysutils;
5.  
6. function  system(s:pchar):integer ; cdecl external 'msvcrt.dll' name 'system';
7.  
8.  
9.  function filelength(filename:ansistring):longword;
10. Var F : File Of byte;
11. var L:longword;
12. begin
13. Assign (F,filename);
14.   Reset (F);
15.   L:=FileSize(F);
16.   Close (F);
17.   exit(L);
18. end;
19.  
20.  
21.  function loadfile(filename:ansistring):ansistring;
22.    Var Fin : File;
23.    Var x:longint;
24.    var content:ansistring='';
25.    begin
26.    x:=filelength(filename);
27.    setlength(content,x);
28.    Assign (Fin,filename);
29.    Reset (Fin,x);
30.    BlockRead (Fin,content[1],1);
31.    close(fin);
32.    exit(content);
33. end;
34.  
35.  procedure savefile(s:ansistring ;filename:ansistring);
36.     var
37.     fout:file;
38.     begin
39.     Assign(fout,filename);
40.     Rewrite(fout,length(s));
41.     blockwrite(fout,s[1],1);
42.     close(fout);
43.   end;
44.  
45.  
46.  
47. var
48. code:ansistring;
49. pas:ansistring;
50. s:ansistring;
51.  
52.  
53. begin
54. pas:=getcurrentdir+'\heloo.pas';
55.  
56. code:='var x,y:integer;'+chr(10);
57. code:=code +'begin'+chr(10);
58. code:=code+'y:=0;'+chr(10);
59. code:=code+' x:= 1 div y;'+chr(10);
60. code:=code+'readln;'+chr(10);
61. code:=code+'end.';
62.  
63.  
64. savefile(code,pas);
65. writeln(loadfile(pas));
66. writeln(fileexists(pas));
67. writeln;
68. writeln;
69.  
70. system(pchar('fpc -vwnhi '+ pas));
71.  
72. system(pchar('cmd /c '+getcurrentdir+'\heloo.exe' +'& pause'));
73.  
74. end.
75.  
76.  
77.  

[ccrause]

I was hoping that it would be easier to intercept error messages than putting everything in a large try catch.

The developer is responsible for handling errors so in those cases it does output something it is your own fault 

But since you changed the requirement to handling unhandled  exceptions:

Code: Pascal  [Select][+][-]

1.   System.ExceptProc:= @CatchNonHandledExceptions;

As TRon mentioned, you can hook into ExceptProc to catch unhandled exceptions. You can also hook into ErrorProc to catch runtime errors.  This way you can customize the generated output.

[rishav]

Thank you @ccrause and @TRon. I think ExceptProc and ErrorProc are exactly what I was looking for.

[Thaddy]

AssignStream?
https://www.freepascal.org/docs-html/rtl/unix/assignstream.html

The text types are simply the handles for stdin/out/err
Linux only.