PHP set_file_buffer Function

last modified April 3, 2025

The PHP set_file_buffer function sets the buffering for file writes. It controls how much data is buffered before being written to disk.

Basic Definition

The set_file_buffer function sets the buffer size for file writes. It takes two parameters: the file pointer and the buffer size in bytes.

Syntax: set_file_buffer(resource $stream, int $size): int. It returns 0 on success, or another value if buffering couldn’t be set.

Basic set_file_buffer Example

This shows how to set a buffer size for a file write operation.

basic_buffer.php

<?php

declare(strict_types=1);

$file = fopen(“output.txt”, “w”); $bufferSize = 8192; // 8KB buffer

$result = set_file_buffer($file, $bufferSize);

if ($result === 0) { fwrite($file, str_repeat(“A”, 10000)); fclose($file); echo “File written with 8KB buffer”; }

This sets an 8KB buffer for writing to output.txt. The buffer accumulates data until it’s full or the file is closed, then writes to disk.

Disabling Buffering

Setting buffer size to 0 disables buffering, forcing immediate writes.

no_buffer.php

<?php

declare(strict_types=1);

$file = fopen(“immediate.txt”, “w”); set_file_buffer($file, 0);

for ($i = 0; $i < 10; $i++) { fwrite($file, “Line $i\n”); sleep(1); // Each write appears immediately }

fclose($file); echo “File written with no buffering”;

With buffering disabled, each write operation immediately hits the disk. This is useful when you need data to persist right away.

Large Buffer for Big Files

Larger buffers can improve performance when writing big files.

large_buffer.php

<?php

declare(strict_types=1);

$file = fopen(“bigfile.dat”, “w”); set_file_buffer($file, 1048576); // 1MB buffer

for ($i = 0; $i < 10000; $i++) { fwrite($file, str_repeat(“DATA”, 100)); }

fclose($file); echo “Large file written with 1MB buffer”;

A 1MB buffer reduces disk I/O operations when writing large amounts of data. Fewer larger writes are generally more efficient than many small ones.

Checking Buffer Setting

You can verify the buffer size was set correctly.

check_buffer.php

<?php

declare(strict_types=1);

$file = fopen(“test.txt”, “w”); $desiredSize = 4096;

$result = set_file_buffer($file, $desiredSize);

if ($result === 0) { echo “Buffer set to $desiredSize bytes successfully”; } else { echo “Failed to set buffer size”; }

fclose($file);

This checks if the buffer was set successfully. A return value of 0 indicates success, while other values mean the buffer couldn’t be set as requested.

Default Buffer Size

This example demonstrates the default buffer behavior.

default_buffer.php

<?php

declare(strict_types=1);

$file1 = fopen(“default1.txt”, “w”); $file2 = fopen(“default2.txt”, “w”);

// Don’t set buffer on file1 set_file_buffer($file2, 0);

fwrite($file1, “Buffered write”); fwrite($file2, “Immediate write”);

fclose($file1); fclose($file2);

echo “Compare file modification times”;

The first file uses PHP’s default buffering, while the second has none. The second file’s content will appear on disk immediately after the write.

Best Practices

• Performance: Larger buffers improve write performance.

• Reliability: Smaller buffers reduce data loss risk.

• Defaults: Understand your system’s default buffer size.

• Testing: Benchmark different sizes for your use case.

Source

PHP set_file_buffer Documentation

This tutorial covered the PHP set_file_buffer function with practical examples showing its usage in different scenarios.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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