Delphi 7 Dynamic Linking

In object pascal for Windows a DLL can be linked into a unit at compile time and at runtime.

Compile Time Dyanamic Linking

The DLL will be loaded by the operating system and linked when the programme is started.

unit sqlite3;

interface

function sqlite3_open(filename: PChar; ctx: Pointer): Integer;
    cdecl; external 'sqlite3.dll';
function sqlite3_close(ctx: Cardinal): Integer; cdecl;
    external 'sqlite3.dll';

implementation

end.

cdecl is for the calling convention used, it is often stdcall for system dlls.

Runtime Dynamic Linking

The DLL will be opened loaded into the process virtual address space when LoadLibrary is called and each function must be assigned individually via GetProcAddress.

unit sqlite3;

interface

var
  sqlite3_open : function(filename: PChar; ctx: Pointer): Integer; cdecl;
  sqlite3_close : function(ctx: Cardinal): Integer; cdecl;

function sqlite3_loadlibrary: Integer;
function sqlite3_freelibrary: Integer;

implementation

uses
  Windows;

var
  sqlite3_handle: Cardinal;

function sqlite3_loadlibrary: Integer;
begin
  sqlite3_handle := LoadLibrary('sqlite3.dll');
  sqlite3_open := GetProcAddress(sqlite3_handle, 'sqlite3_open');
  sqlite3_close := GetProcAddress(sqlite3_handle, 'sqlite3_close');
end;

function sqlite3_freelibrary: Integer;
begin
  FreeLibrary(sqlite3_handle);
end;

cdecl is for the calling convention used, it is often stdcall for system dlls.

References

For the DLL used in this example see SQLite3 Compile Windows DLL.