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Archive for July 14th, 2011

Delphi commandline oddity with double-quoted arguments

Posted by jpluimers on 2011/07/14

Boy, I was wrong. Somewhere in the back of my head I knew it.

ParamStr goes from zero (the name of the EXE) through ParamCount (the last parameter). Duh :)

 

I’ll keep this so you can have a good laugh:

 

When you add double quoted arguments to the commandline of your Delphi app, strange things can happen: the first parameter seems to be gone, while it is there.

It appears that the ParamCount/ParamStr logic fails here, and cannot be repaired because of backward compatibility.

Lets look at this commandline:

“..\bin\DumpCommandLine.exe” “C:\Program Files\test.xml” “C:\Program Files\meMySelfAndI.xml”

The demo code below will output something like this:

ParamCount:     2
ParamStr():
0       C:\develop\DumpCommandLine\bin\DumpCommandLine.exe
1       C:\Program Files\test.xml
CommandLine:
"..\bin\DumpCommandLine.exe" "C:\Program Files\test.xml" "C:\Program Files\meMySelfAndI.xml"
CommandLineStrings.Count:       3
CommandLineStrings[]:
0       ..\bin\DumpCommandLine.exe
1       C:\Program Files\test.xml
2       C:\Program Files\meMySelfAndI.xml

You see that regular ParamCount/ParamStr calls will mis the “C:\Program Files\test.xml” parameter.
But getting it through CommandLineStrings will correctly get it.

This is the dump code:

unit CommandlineDemoUnit;

interface

procedure DumpCommandLineToConsole;

implementation

uses
  Classes, CommandlineUnit;

procedure DumpCommandLineToConsole;
var
  CommandLineStrings: TStrings;
  I: Integer;
begin
  Writeln('ParamCount:', #9, ParamCount);
  Writeln('ParamStr():');
  for I := 0 to ParamCount - 1 do
    Writeln(I, #9, ParamStr(I));
  Writeln('CommandLine:');
  Writeln(CommandLine);
  CommandLineStrings := CreateCommandLineStrings();
  Writeln('CommandLineStrings.Count:', #9, CommandLineStrings.Count);
  Writeln('CommandLineStrings[]:');
  try
    for I := 0 to CommandLineStrings.Count - 1 do
      Writeln(I, #9, CommandLineStrings[I]);
  finally
    CommandLineStrings.Free;
  end;
end;

end.

And this the code to get the CommandLine and CommandLineStrings, which will fill a TStrings result using the CommaText property (it uses a default QuoteChar of of double quote #34 and Delimiter of space #32, this will work nicely):

unit CommandlineUnit;

interface

uses
  Classes;

function CommandLine: string;
function CreateCommandLineStrings: TStrings;

implementation

uses
  Windows;

function CommandLine: string;
begin
  Result := GetCommandLine();
end;

function CreateCommandLineStrings: TStrings;
begin
  Result := TStringList.Create();
  Result.CommaText := CommandLine;
end;

end.

Note that you need to manually free the TStrings object to avoid memory leaks.

–jeroen

Posted in Delphi, Development, Software Development | 13 Comments »

 
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