Fix BIFF8 DIMENSIONS record to use 0-based column indices

CHANGELOG.md

@@ -44,6 +44,7 @@ and this project adheres to [Semantic Versioning](https://semver.org). Thia is a
 - Missing array key x for Xlsx Reader VML. [Issue #4505](https://github.com/PHPOffice/PhpSpreadsheet/issues/4505) [PR #4676](https://github.com/PHPOffice/PhpSpreadsheet/pull/4676)
 - Better support for Style Alignment Read Order. [Issue #850](https://github.com/PHPOffice/PhpSpreadsheet/issues/850) [PR #4655](https://github.com/PHPOffice/PhpSpreadsheet/pull/4655)
 - More sophisticated workbook password algorithms (Xlsx only). [Issue #4673](https://github.com/PHPOffice/PhpSpreadsheet/issues/4673) [PR #4675](https://github.com/PHPOffice/PhpSpreadsheet/pull/4675)
+- Xls Writer fix DIMENSIONS record. [Issue #4682](https://github.com/PHPOffice/PhpSpreadsheet/issues/4682) [PR #4687](https://github.com/PHPOffice/PhpSpreadsheet/pull/4687)
 
 ## 2025-09-03 - 5.1.0
 

src/PhpSpreadsheet/Writer/Xls/Worksheet.php

@@ -211,15 +211,14 @@ public function __construct(int &$str_total, int &$str_unique, array &$str_table
         $maxC = $this->phpSheet->getHighestColumn();
 
         // Determine lowest and highest column and row
-        $this->firstRowIndex = $minR;
-        $this->lastRowIndex = ($maxR > 65535) ? 65535 : $maxR;
-
-        $this->firstColumnIndex = Coordinate::columnIndexFromString($minC);
-        $this->lastColumnIndex = Coordinate::columnIndexFromString($maxC);
-
-        if ($this->lastColumnIndex > 255) {
-            $this->lastColumnIndex = 255;
-        }
+        // BIFF8 DIMENSIONS record requires 0-based indices for both rows and columns
+        // Row methods return 1-based values (Excel UI), so subtract 1 to convert to 0-based
+        $this->firstRowIndex = $minR - 1;
+        $this->lastRowIndex = ($maxR > 65536) ? 65535 : ($maxR - 1);
+
+        // Column methods return 1-based values (columnIndexFromString('A') = 1), so subtract 1
+        $this->firstColumnIndex = Coordinate::columnIndexFromString($minC) - 1;
+        $this->lastColumnIndex = min(255, Coordinate::columnIndexFromString($maxC) - 1);
         $this->writerWorkbook = $writerWorkbook;
     }
 
@@ -258,7 +257,8 @@ public function close(): void
         }
 
         $columnDimensions = $phpSheet->getColumnDimensions();
-        $maxCol = $this->lastColumnIndex - 1;
+        // lastColumnIndex is now 0-based, so no need to subtract 1
+        $maxCol = $this->lastColumnIndex;
         for ($i = 0; $i <= $maxCol; ++$i) {
             $hidden = 0;
             $level = 0;

tests/PhpSpreadsheetTests/Writer/Xls/DimensionsRecordTest.php

@@ -0,0 +1,129 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PhpOffice\PhpSpreadsheetTests\Writer\Xls;
+
+use PhpOffice\PhpSpreadsheet\Spreadsheet;
+use PhpOffice\PhpSpreadsheet\Writer\Xls;
+use PHPUnit\Framework\TestCase;
+
+class DimensionsRecordTest extends TestCase
+{
+    /**
+     * Test that DIMENSIONS record uses 0-based indices for both rows and columns.
+     *
+     * This test verifies that the BIFF8 DIMENSIONS record correctly uses 0-based
+     * indices for both rows and columns. Prior to the fix, 1-based values were
+     * written directly to the DIMENSIONS record, causing issues with old XLS parsers
+     * that expect 0-based indices per the BIFF8 specification.
+     *
+     * The DIMENSIONS record structure (BIFF8):
+     * - Offset 0-3: Index to first used row (0-based)
+     * - Offset 4-7: Index to last used row + 1 (0-based)
+     * - Offset 8-9: Index to first used column (0-based)
+     * - Offset 10-11: Index to last used column + 1 (0-based)
+     * - Offset 12-13: Not used
+     *
+     * Note: All indices in the DIMENSIONS record are 0-based, meaning Excel row 1
+     * is stored as 0, row 5 as 4, column A as 0, column D as 3, etc.
+     */
+    public function testDimensionsRecordUsesZeroBasedColumnIndices(): void
+    {
+        $spreadsheet = new Spreadsheet();
+        $sheet = $spreadsheet->getActiveSheet();
+
+        // Set values in columns A through D (should be indices 0-3 in 0-based)
+        $sheet->setCellValue('A1', 'Column A');
+        $sheet->setCellValue('B1', 'Column B');
+        $sheet->setCellValue('C1', 'Column C');
+        $sheet->setCellValue('D1', 'Column D');
+        $sheet->setCellValue('A5', 'Row 5');
+
+        // Write to XLS format
+        $filename = tempnam(sys_get_temp_dir(), 'phpspreadsheet-test-');
+        $writer = new Xls($spreadsheet);
+        $writer->save($filename);
+        $spreadsheet->disconnectWorksheets();
+
+        // Read the binary file and find the DIMENSIONS record
+        $fileContent = file_get_contents($filename);
+        self::assertIsString($fileContent, 'Failed to read XLS file');
+        unlink($filename);
+
+        // Find the DIMENSIONS record: 0x0200 (2 bytes) + length 0x000E (2 bytes)
+        $recordSignature = pack('v', 0x0200) . pack('v', 0x000E);
+        $pos = strpos($fileContent, $recordSignature);
+
+        self::assertIsInt($pos, 'DIMENSIONS record not found in XLS file');
+
+        // Parse the DIMENSIONS record (skip 4-byte header)
+        $dataPos = $pos + 4;
+        $dimensionsData = substr($fileContent, $dataPos, 14);
+
+        // Unpack DIMENSIONS record
+        $data = unpack('VrwMic/VrwMac/vcolMic/vcolMac/vreserved', $dimensionsData);
+        self::assertIsArray($data, 'Failed to unpack DIMENSIONS record');
+
+        // Verify the values are correct (0-based for both rows and columns)
+        // First used row is 1 (Excel UI), which is 0 in 0-based indexing
+        self::assertSame(0, $data['rwMic'], 'First row should be 0 (0-based)');
+
+        // Last used row is 5 (Excel UI), which is 4 in 0-based, so rwMac should be 5 (4 + 1)
+        self::assertSame(5, $data['rwMac'], 'Last row + 1 should be 5 (0-based row 4 + 1)');
+
+        // First column is A (Excel UI), which is 0 in 0-based indexing
+        // BEFORE FIX: This would be 1 (because columnIndexFromString('A') returns 1)
+        // AFTER FIX: This is 0 (because we subtract 1)
+        self::assertSame(0, $data['colMic'], 'First column should be 0 (0-based for column A)');
+
+        // Last column is D (Excel UI), which is 3 in 0-based, so colMac should be 4 (3 + 1)
+        // BEFORE FIX: This would be 5 (columnIndexFromString('D') = 4, not adjusted to 0-based)
+        // AFTER FIX: This is 4 (columnIndexFromString('D') - 1 = 3, + 1 = 4)
+        self::assertSame(4, $data['colMac'], 'Last column + 1 should be 4 (0-based column 3 + 1)');
+    }
+
+    /**
+     * Test that DIMENSIONS record correctly handles columns near the BIFF8 limit.
+     *
+     * BIFF8 format supports columns up to IV (256 columns, 0-based index 0-255).
+     * This test ensures that the lastColumnIndex is correctly capped at 255.
+     */
+    public function testDimensionsRecordCapsColumnIndexAt255(): void
+    {
+        $spreadsheet = new Spreadsheet();
+        $sheet = $spreadsheet->getActiveSheet();
+
+        // Set value in column IV (column 256, 0-based index 255)
+        $sheet->setCellValue('IV1', 'Last BIFF8 Column');
+
+        // Write to XLS format
+        $filename = tempnam(sys_get_temp_dir(), 'phpspreadsheet-test-');
+        $writer = new Xls($spreadsheet);
+        $writer->save($filename);
+        $spreadsheet->disconnectWorksheets();
+
+        // Read the binary file and find the DIMENSIONS record
+        $fileContent = file_get_contents($filename);
+        self::assertIsString($fileContent, 'Failed to read XLS file');
+        unlink($filename);
+
+        // Find the DIMENSIONS record: 0x0200 (2 bytes) + length 0x000E (2 bytes)
+        $recordSignature = pack('v', 0x0200) . pack('v', 0x000E);
+        $pos = strpos($fileContent, $recordSignature);
+
+        self::assertIsInt($pos, 'DIMENSIONS record not found in XLS file');
+
+        // Parse the DIMENSIONS record (skip 4-byte header)
+        $dataPos = $pos + 4;
+        $dimensionsData = substr($fileContent, $dataPos, 14);
+
+        // Unpack DIMENSIONS record
+        $data = unpack('VrwMic/VrwMac/vcolMic/vcolMac/vreserved', $dimensionsData);
+        self::assertIsArray($data, 'Failed to unpack DIMENSIONS record');
+
+        // Last column should be capped at 256 (255 + 1 for "last used + 1")
+        // The min(255, ...) ensures we don't exceed the BIFF8 limit
+        self::assertLessThanOrEqual(256, $data['colMac'], 'Last column index should not exceed 256');
+    }
+}