Why Am I Getting the "FPDF error: Some data has already been output, can't send PDF" Message?

FPDF Output Error: "Some Data Has Already Been Output"

Issue:

When using the FPDF library in PHP, the following error is encountered: "FPDF error: Some data has already been output, can't send PDF."

Analysis:

This error occurs when FPDF detects any output prior to the PDF generation process. FPDF strictly requires the absence of any extraneous output to prevent potential conflicts. This includes leading or trailing spaces, comments, or any other non-PDF content.

Solution:

To resolve this issue, ensure that the FPDF library is the first and only output generated by your PHP script. This means eliminating any leading spaces or other extraneous content before the FPDF code block.

<?php
$pdf = new FPDF();
$pdf->AddPage();
$pdf->SetFont('Arial', 'B', 16);
$pdf->Cell(40, 10, 'Hello World!');
$pdf->Output();
?>

Additional Recommendations:

• Separate File Format: Create a separate PHP file for the PDF generation task to isolate it from any other potential output sources.
• Verify Environment: Double-check your server configuration to ensure that it is not automatically adding any output, such as through configuration directives.
• Alternative PDF Library: If FPDF continues to encounter output issues, consider using an alternative PDF library that may be more compatible with Drupal.

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