Manipulate INI files from Delphi

The .INI files have a text-based file format for representing application configuration data.

Even though, Windows Microsoft recommends using Registry to store application specific configuration data, in many cases you'll find that using INI files is much faster. After all, Windows still use WIN.INI and SYSTEM.INI files.

One simple use of INI files, as a status saving mechanism, would be to save the size and location of a form if you want a form to reappear at its previous position.

.INI file format

Initialization or Configuration Settings file (.INI) is a text file with 64Kb limit divided into sections, each containing zero or more keys. Each key contains zero or more values. Example:

[SectionName]
keyname1=value
;comment
keyname2=value

Section names are enclosed in square brackets, and must begin at the beginning of a line. Section and key names are case-insensitive, and cannot contain spacing characters. The key name is followed by an equal sign ("="), optionally surrounded by spacing characters, which are ignored.

If the same section appears more than once in the same file, or if the same key appears more than once in the same section, then the last occurrence prevails.

A key can contain string, integer or boolean value.

Delphi IDE uses INI file format in many cases. For example, the .DSK files (desktop settings) have the INI file format.

TIniFile

Delphi provides the TIniFile class, declared in the inifiles.pas unit, with methods to store and retrieve values from INI files. Prior to working with the TIniFile methods you need to create an instance of the class:

uses inifiles;
...
var
  IniFile : TIniFile;
begin
  IniFile := TIniFile.Create('myapp.ini') ;

The above code creates an IniFile object and assigns 'myapp.ini' to the only property of the class - the FileName property - used to specify the name of the INI file you are to use.

The code as written above looks (stores) for the myapp.ini file in the \Windows directory. A better way to store application data is in the application's folder - just specify the full path name of the file for the Create method:

// place the INI in the application folder,
// let it have the application name
// and 'ini' for extension:

iniFile := TIniFile.Create(ChangeFileExt(Application.ExeName,'.ini')) ;

Read from INI

The TIniFile class has several "read" methods. The ReadString reads a string value from a key, ReadInteger, ReadFloat and similiar are used to read a number from a key. All "read" methods have a default value that can be used if the entry does not exist. For example the ReadString is declared as:

function ReadString(const Section, Ident, Default: String): String; override;

Write to INI

The TIniFile has a corresponding "write" method for each "read" method. In other words they are WriteString, WriteBool, WriteInteger, etc.

For example, if we want a program to remember the name of the last person who used it, when it was, and what were the main form coordinates, we might establish a section called "Users" and a keyword called "Last" and "Date" to track the information; and another section called "Placement" with keys "Top", "Left", "Width", "Height".

project1.ini

 [User]
 Last=Zarko Gajic
 Date=01/29/2009
 [Placement]
 Top=20
 Left=35
 Width=500
 Height=340

Note that the key named "Last" holds a string value, "Date" holds a TDateTime value, all keys in the "Placement" section hold an integer value.

The OnCreate event of the main form is the perfect place to store the code needed to access the values in the application's initialization file:

procedure TMainForm.FormCreate(Sender: TObject) ;
var
  appINI : TIniFile;
  LastUser : string;
  LastDate : TDateTime;
begin
  appINI := TIniFile.Create(ChangeFileExt(Application.ExeName,'.ini')) ;
  try
    //if no last user return an empty string
    LastUser := appINI.ReadString('User','Last','') ;
    //if no last date return todays date
    LastDate := appINI.ReadDate('User', 'Date', Date) ;

    //show the message
    ShowMessage('This program was previously used by ' + LastUser + ' on ' + DateToStr(LastDate));

    Top := appINI.ReadInteger('Placement','Top', Top) ;
    Left := appINI.ReadInteger('Placement','Left', Left);
    Width := appINI.ReadInteger('Placement','Width', Width);
    Height := appINI.ReadInteger('Placement','Height', Height);
  finally
    appINI.Free;
  end;
end;

Main form's OnClose event is ideal for the "Save INI" part of the project.

procedure TMainForm.FormClose(Sender: TObject; var Action: TCloseAction) ;
var
  appINI : TIniFile;
begin
  appINI := TIniFile.Create(ChangeFileExt(Application.ExeName,'.ini')) ;
try
    appINI.WriteString('User','Last','Zarko Gajic') ;
    appINI.WriteDate('User', 'Date', Date) ;

    with appINI, MainForm do
    begin
      WriteInteger('Placement','Top', Top) ;
      WriteInteger('Placement','Left', Left) ;
      WriteInteger('Placement','Width', Width) ;
      WriteInteger('Placement','Height', Height) ;
    end;
  finally
    appIni.Free;
  end;
end;

INI Sections

The EraseSection erases an entire section of an INI file. The ReadSection and ReadSections fills a TStringList object with the names of all sections (and key names) in the INI file.

INI Limitations and Downsides

The TIniFile class uses the Windows API which imposes a limit of 64KB on INI files. If you need to store more than 64KB of data, you should use the TMemIniFile.

Another problem might rise if you have a section with more than 8K value. One way to solve the problem is to write your own version of the ReadSection method.

Check ut "where should I store my application's data".