How to include functions or procedures in Pascal through an existing archive?

Question

I’m new to Pascal and I’m looking for how to call functions or procedures from an existing archive in Pascal.

There is a function in Julia called include('filename.jl') where I add functions already written in a previously made notepad so I can use them while running the compiler.

I wonder if there is such an application in Pascal. If so, how should I write in the text file? Could you give me a clear example of your application? I’m looking for good hours how to do this, but nothing satisfying.

Answer 1

You can use build directives. Example taken from the documentation of Free Pascal.

unit testi;

interface

{$I *}

implementation

end.

In this example, the compiler will look for a file called testi or testi.pp and will "paste" where the compilation directive is {$I}.

The compiler will search your file in the following places:

• location specified in the Directive
• in the current directory
• all directories specified in the search directory (you can add directories to the search directory using the option -Fi command line)

Some care to be taken:

• The name of unit has to be the same file name.
• You can include files within other files, but not infinitely. The maximum number is restricted by the number of file descriptors available to the Free Pascal compiler.
• Unlike the Turbo Pascal, you can include cross blocks. I mean, a file can open a Begin and in another file to be included close the block with End.

Answer 2

A Delphi application is divided into Units. Each Unit is a language source code file Objectpascal (is not the default pascal), where several language constructs can be declared, such as isolated types and procedures. So that a Unit can have access to constructions declared in another, there is a session called uses. This session contains the list of which Units must be consulted so that the symbols are recognised and resolved by the compiler.

So if there are two Units declared (Unit1 and Unit2), why Unit1 make use of existing symbols in Unit2, is as set forth below.

Unit1

unit Unit1;

interface

uses
  Unit2;

type
  TClasse1 = class(TClasse2)
  end;

implemetation

end.

Unit2

unit Unit2;

interface

type
  TClasse2 = class
  end;

implementation

end.

In this example, Unit2 declares a guy named TClasse2 which will be used in Unit1 to declare another type, called TClasse1.

Unit1 needs to exist in a file called Unit1.pas and Unit2 needs to exist in a file called Unit2.pas.

Answer 3

I’ll answer again with an idea clearer than me think that you want.

You can use a library file of functions and procedures. For example:

Library - with a single function that extracts a substring SubStr

library subs; 

function SubStr(CString: PChar;FromPos,ToPos: Longint): PChar; cdecl; 

var 
  Length: Integer; 

begin 
  Length := StrLen(CString); 
  SubStr := CString + Length; 
  if (FromPos > 0) and (ToPos >= FromPos) then 
  begin 
    if Length >= FromPos then 
      SubStr := CString + FromPos - 1; 
    if Length > ToPos then 
    CString[ToPos] := #0; 
  end; 
end; 

exports 
  SubStr; 

end.

Using the library

program testsubs; 

function SubStr(const CString: PChar; FromPos, ToPos: longint): PChar; 
  cdecl; external ’subs’; 

var 
  s: PChar; 
  FromPos, ToPos: Integer; 
begin 
  s := ’Test’; 
  FromPos := 2; 
  ToPos := 3; 
  WriteLn(SubStr(s, FromPos, ToPos)); 
end.