FPSpreadsheet

Because of it's very simple format, it's easy to generate Excel 2.1 files from code. New Excel versions are still capable of reading those files, so this can be enough to automate the generation of simple Excel files. Unfortunately Excel 4 and older formats don't support multiple sheets in the same file, so this isn't supported by this method.

Here is a unit which can write Excel 2.1 files:

{
excel2utils.pas

Writes an Excel 2.1 file

To write the file, always start calling StartExcel2File to create the Excel
file header, then call WriteExcel2Cell once for each cell value and finally
call EndExcel2File to write the end of the file.

License: The same modifyed LGPL as the Lazarus Component Library

AUTHORS: Felipe Monteiro de Carvalho
}
unit excel2utils;

{$ifdef fpc}
{$mode delphi}{$H+}
{$endif}

interface

uses
  Classes, SysUtils; 

const
  STR_EXCEL_EXTENSION = '.xls';

procedure WriteExcel2Cell(AStream: TStream; const ACol, ARow: Word; const AValue: string);
procedure StartExcel2File(AStream: TStream);
procedure EndExcel2File(AStream: TStream);

implementation

procedure WriteExcel2Cell(AStream: TStream; const ACol, ARow: Word;
 const AValue: string);
var
  L: Word;
  CXlsLabel: array[0..5] of Word = ($204, 0, 0, 0, 0, 0);
begin
  L := Length(AValue);
  CXlsLabel[1] := 8 + L;
  CXlsLabel[2] := ARow;
  CXlsLabel[3] := ACol;
  CXlsLabel[5] := L;
  AStream.WriteBuffer(CXlsLabel, SizeOf(CXlsLabel));
  AStream.WriteBuffer(Pointer(AValue)^, L);
end;

procedure StartExcel2File(AStream: TStream);
var
  CXlsBof: array[0..5] of Word = ($809, 8, 0, $10, 0, 0);
begin
  AStream.WriteBuffer(CXlsBof, SizeOf(CXlsBof));
end;

procedure EndExcel2File(AStream: TStream);
var
  CXlsEof: array[0..1] of Word = ($0A, 00);
begin
  AStream.WriteBuffer(CXlsEof, SizeOf(CXlsEof));
end;

end.

And here is an example of how to use it:

{
excel2demo.dpr

Demonstrates how to write an Excel 2.1 file using the excel2utils unit

Public Domain

AUTHORS: Felipe Monteiro de Carvalho
}
program excel2demo;

{$mode delphi}{$H+}

uses
  Classes, SysUtils;

var
  OutputFile: TFileStream;
  MyDir: string;
begin
  // Open the output file
  MyDir := ExtractFilePath(ParamStr(0));
  OutputFile := TFileStream.Create(MyDir + 'test' + STR_EXCEL_EXTENSION, fmCreate or fmOpenWrite);
  StartExcel2File(OutputFile);

  // Write some cells
  WriteExcel2Cell(OutputFile, 0, 0, '1');
  WriteExcel2Cell(OutputFile, 1, 0, '2');
  WriteExcel2Cell(OutputFile, 2, 0, '3');
  WriteExcel2Cell(OutputFile, 3, 0, '4');

  // Close the files
  EndExcel2File(OutputFile);
  OutputFile.Free;
end.