Exception.Create Constructor

Instantiates an instance of an exception with a simple message string.

Pascal

constructor Create(const Msg: string);

C++

__fastcall Exception(const AnsiString Msg);

Description

Call Create to construct an exception object with a simple message string.

Msg is the string containing the runtime error message to display in the exception dialog box. Msg can be a hard-coded string, or can be a function call that returns a string.

C++ Examples:

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/*
The following example creates a directory ‘C:\temp’ if it
does not already exist.
}
*/
#include <Filectrl.hpp>
void __fastcall TForm1::Button1Click(TObject *Sender)
{
  if (!DirectoryExists("c:\\temp"))
  {
    if (!CreateDir("C:\\temp"))
      throw Exception("Cannot create c:\\temp directory.");
  }
  if (!CreateDir("C:\\temp"))
    throw Exception("Cannot create C:\\temp again!");
}

Delphi Examples:

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{
The following example creates a directory ‘C:\temp’ if it
does not already exist.
}
uses FileCtrl;
procedure TForm1.Button1Click(Sender: TObject);
begin
  if not SysUtils.DirectoryExists('C:\temp') then
    if not CreateDir('C:\temp') then
      raise Exception.Create('Cannot create C:\temp');
  if not CreateDir('C:\temp') then
    raise Exception.Create('Cannot create C:\temp again!');
end;

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{
The following example uses a button, a string grid, and a
Save dialog box on a form. When the button is clicked, the
user is prompted for a filename. When the user clicks OK,
the contents of the string grid are written to the specified
file. Additional information is also written to the file so
that it can be read easily with the FileRead function.
} 
procedure TForm1.Button1Click(Sender: TObject);
var
  BackupName: string;
  FileHandle: Integer;
  StringLen: Integer;
  X, Y, I: Integer;
  colCountLength, rowCountLength: Integer;
  Buffer: PChar;
  cellString: string;
begin
  if SaveDialog1.Execute then
  begin
    if FileExists(SaveDialog1.FileName) then
    begin
      BackupName := SysUtils.ExtractFileName(SaveDialog1.FileName);
      BackupName := ChangeFileExt(BackupName, '.BAK');
      if not RenameFile(SaveDialog1.FileName, BackupName) then
        raise Exception.Create('Unable to create backup file.');
    end;
    FileHandle := FileCreate(SaveDialog1.FileName);
    { Write out the number of rows and columns in the grid. }
    colCountLength := SizeOf(StringGrid1.ColCount);
    FileWrite(FileHandle, 
      Pchar(StringGrid1.ColCount), colCountLength);
    rowCountLength := SizeOf(StringGrid1.RowCount);
    FileWrite(FileHandle,
      PChar(StringGrid1.RowCount), rowCountLength);
    for X := 0 to StringGrid1.ColCount - 1 do
    begin
      for Y := 0 to StringGrid1.RowCount - 1 do
      begin
        try
          { Write out the length of each string, followed by the string itself. }
          StringLen := Length(StringGrid1.Cells[X,Y]);
          FileWrite(FileHandle, PChar(StringLen), SizeOf(StringLen));
          GetMem(Buffer, StringLen); { allocate the buffer }
          cellString := StringGrid1.Cells[X,Y];
          for I := 1 to StringLen do
             Buffer[I - 1] := cellString[I];
          FileWrite(FileHandle, Buffer^, StringLen);
        finally
          FreeMem(Buffer, StringLen);
        end;
      end;
    end;
    FileClose(FileHandle);
  end;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  with StringGrid1 do
  begin
    Cells[1,0] := 'Column 1';
    Cells[2,0] := 'Column 2';
    Cells[3,0] := 'Column 3';
    Cells[4,0] := 'Column 4';
    Cells[0,1] := 'Row 1';
    Cells[1,1] := 'Object';
    Cells[2,1] := 'Pascal';
    Cells[3,1] := 'is';
    Cells[4,1] := 'excellent';
    Cells[0,2] := 'Row 2';
    Cells[1,2] := 'Delphi';
    Cells[2,2] := 'is';
    Cells[4,2] := 'RAD';
  end;
end;

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{
In addition to displaying the exception message, which 
happens by default, the following code shuts down the 
application when an exception is not caught and handled.  
AppException should be declared a method of TForm1.
}
procedure TForm1.FormCreate(Sender: TObject);
begin
  Application.OnException := AppException;
end;

procedure TForm1.AppException(Sender: TObject; E: Exception);
begin
  Application.ShowException(E);
  Application.Terminate;
end; 

procedure TForm1.Button1Click(Sender: TObject);
begin
  raise EPasswordInvalid.Create('Incorrect password entered');
end;