PHPExcel unable to open the saved file - php

Question

I am trying to open an existing excel file, modify some cells and save it. I am using Excel2007 for reader and writer.
The input file is about 1 MB large and it has few formulas, protected data and hidden rows and columns and worksheets which I do not modify.
I am able to load the data and read and write some values into it, which I check with various var_dumps in the code.
The problem is while saving it. It throws some fatal errors on timing outs and also if it writes the file the file size is bloated to 9.2 MB, which is okay if I can open it.
code snippet - nothing fancy.
$objReader = PHPExcel_IOFactory::createReader('Excel2007');
$objPHPExcel = $objReader->load($inputFile);
$objPHPExcel->setActiveSheetIndex(2);
$activeSheet = $objPHPExcel->getActiveSheet();
$currCell = $activeSheet->getCell("O3");
$cellValidation = $currCell->getDataValidation("O3");
$values = array();
if ($cellValidation->getShowDropDown() == true)
{
$values = $cellValidation->getFormula1();
$valArray = explode(",", $values);
$currCell->setValue($valArray[0]);
}
$objWriter = PHPExcel_IOFactory::createWriter($objPHPExcel, 'Excel2007');
$objWriter -> setPreCalculateFormulas(false);
$objWriter->save($outputFile);
I use MS Excel 2010 to open the resultant file but it just takes forever and has not opened it even once.
Please help me to troubleshoot this by giving me pointers as to where I should be looking.
Any help is greatly appreciated.

Answer 1

Instead of saving it to a file, save it to php://output­Docs:
$objWriter->save('php://output');
This will send it AS-IS to the browser.
You want to add some headers­Docs first, like it's common with file downloads, so the browser knows which type that file is and how it should be named (the filename):
// We'll be outputting an excel file
header('Content-type: application/vnd.ms-excel');
// It will be called file.xls
header('Content-Disposition: attachment; filename="file.xls"');
// Write file to the browser
$objWriter->save('php://output');
First do the headers, then the save. For the excel headers see as well the following question: Setting mime type for excel document.
So the final code would have below lines -
// Save Excel 2007 file
#echo date('H:i:s') . " Write to Excel2007 format\n";
$objWriter = PHPExcel_IOFactory::createWriter($objPHPExcel, 'Excel2007');
ob_end_clean();
// We'll be outputting an excel file
header('Content-type: application/vnd.ms-excel');
// It will be called file.xls
header('Content-Disposition: attachment; filename="file.xlsx"');
$objWriter->save('php://output');
I think this line:
ob_end_clean();
Should solve your problem.
Thanks!

Answer 2

There's a whole lot of reasons for that "bloat" and it very much depends on the actual data in the worksheet, but MS Excel itself uses a lot of different techniques to keep the filesize small, whereas PHPExcel writes a simple version of the OfficeOpenXML format.
For example, MS Excel looks at the string content of all cells, and stores the individual strings in a string table. If a string is used by two or more cells, there will only be a single entry in the string table. However, there's a performance overhead in checking if a string already exists in the string table, so PHPExcel doesn't perform that check but will duplicate entries in the string table. This means that it will create a large file because of the duplication, but keeps the save speed as fast as possible.
Similarly, MS Excel looks at all formulae, and if the formula is similar to an existing formula (with only a row/column offset difference) it will store it as a shared formula rather than a cell formula, so the actual formula data is only stored once. Again, PHPExcel won't perform this check, because it is a big performance overhead in the save, so it stores every formula as a cell formula rather than a shared formula.
And no, I can't explain why the file doesn't load in MS Excel 2010, nor will I be able to explain it without being able to run the whole thing through debug