Executing External Programs/nl

Inleiding

Er zijn verschillende manieren om een extern programma uit te laten voeren. We richten ons nu op een manier, namelijk het gebruik van TProcess.

TProcess

TProcess wordt gebruikt om een extern programma uit te laten voeren. Een paar voordelen van het gebruik van TProcess boven andere manieren zijn:

• Platform onafhankelijk.
• Het geeft ook de mogelijkheid om te schrijven naar stdout en te lezen van stdin.

Een eenvoudig voorbeeld

// Dit is een demo prograamma dat laat zien hoe je
// een extern programma kunt uitvoeren.
program launchprogram;

// De te gebruiken units. 
uses 
  Classes, SysUtils, Process;

// This is defining the var "AProcess" as a variable 
// of the type "TProcess"
var 
  AProcess: TProcess;

// This is where our program starts to run
begin
  // Now we will create the TProcess object, and
  // assign it to the var AProcess.
  AProcess := TProcess.Create(nil);

  // Tell the new AProcess what the command to execute is.
  // Let's use the FreePascal compiler
  AProcess.CommandLine := 'ppc386 -h';

  // We will define an option for when the program
  // is run. This option will make sure that our program
  // does not continue until the program we will launch
  // has stopped running.                vvvvvvvvvvvvvv
  AProcess.Options := AProcess.Options + [poWaitOnExit];

  // Now that AProcess knows what the commandline is 
  // we will run it.
  AProcess.Execute;

  // This is not reached until ppc386 stops running.
  AProcess.Free;   
end.

That's it! You have just learned how to run an external program from inside your own program.

That's nice, but how do I read the Output of a program that I have run?

Well, let's expand our example a little and do just that:

An Improved Example

// This is a demo program that shows how to launch
// an external program and read from it's output.
program launchprogram;

// Here we include files that have useful functions
// and procedures we will need.
uses 
  Classes, SysUtils, Process;

// This is defining the var "AProcess" as a variable 
// of the type "TProcess"
// Also now we are adding a TStringList to store the 
// data read from the programs output.
var 
  AProcess: TProcess;
  AStringList: TStringList;

// This is where our program starts to run
begin
  // Now we will create the TProcess object, and
  // assign it to the var AProcess.
  AProcess := TProcess.Create(nil);

  // Create the TStringList object.
  AStringList := TStringList.Create;

  // Tell the new AProcess what the command to execute is.
  // Let's use the FreePascal compiler
  AProcess.CommandLine := 'ppc386 -h';

  // We will define an option for when the program
  // is run. This option will make sure that our program
  // does not continue until the program we will launch
  // has stopped running. Also now we will tell it that
  // we want to read the output of the file.
  AProcess.Options := AProcess.Options + [poWaitOnExit, poUsePipes];

  // Now that AProcess knows what the commandline is 
  // we will run it.
  AProcess.Execute;
  
  // This is not reached until ppc386 stops running.

  // Now read the output of the program we just ran
  // into the TStringList.
  AStringList.Lines.ReadFromStream(AProcess.Output);
  
  // Save the output to a file.
  AStringList.Lines.SaveToFile('c:\output.txt');

  // Now that the file is saved we can free the 
  // TStringList and the TProcess.
  AStringList.Free;
  AProcess.Free;   
end.