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PHP fflush() function (with example)

Hi everyone,

I hope you're all doing well. I have a question regarding the PHP `fflush()` function, and I was wondering if someone could help me out.

So, I have been working on a web application where I need to write data to a file using PHP. I came across the `fflush()` function while looking for ways to ensure that the data is written and saved in the file immediately. However, I'm a bit unsure about how exactly this function works and what its purpose is.

Could someone please explain to me what the `fflush()` function does in PHP and provide an example of how to use it effectively in a web application? I would also appreciate any insights into why and when `fflush()` is particularly useful.

Thank you so much in advance for your kind assistance. I'm looking forward to learning more from the knowledgeable members of this forum.

Best regards,

All Replies


Hey John,

I've used the `fflush()` function in PHP before, so I'd be happy to share my experience with you. In PHP, `fflush()` is primarily used to ensure that any output written to a stream (such as a file) is immediately sent and saved, rather than being buffered.

For instance, if you're writing data to a file using PHP's `fwrite()` function and you want to make sure the content is immediately written to the file, you can follow it up with `fflush()` to flush the output buffer. This can be beneficial in scenarios where you need real-time updating of the file or when you want to make sure that all data is stored before performing any subsequent operations on the file.

Here's a simple example to illustrate its usage:

$file = 'myfile.txt';
$data = "Hello, world!";

$handle = fopen($file, 'w');
fwrite($handle, $data);
fflush($handle); // Flushes the output buffer

In this example, the `fflush($handle)` line ensures that the data written to the file is immediately saved.

One important thing to note is that using `fflush()` excessively can impact performance since it forces the output to be written immediately, causing additional disk I/O operations. Therefore, it's advisable to use it when necessary and in specific cases where the immediate update of the output is required.

I hope this clarifies the usage of `fflush()` in PHP. Feel free to ask any further questions if you have them!

Best regards,


Hey there John,

I noticed you were asking about the PHP `fflush()` function and thought I'd chime in with my experience. So, `fflush()` plays an important role in ensuring the desired behavior of file handling operations.

When working with file streams, PHP tends to buffer the output before actually writing it to the file. This buffering can result in delays or unexpected behavior if you rely on the data being immediately accessible or visible to other processes.

I recently encountered a situation where I had to write logs to a file in real-time for a chat application. Initially, without `fflush()`, the logs weren't visible in the file until a significant amount of data was accumulated or when the script execution ended. This caused a lag in monitoring and debugging the chat system.

By using `fflush()`, I was able to force the immediate writing of the log data to the file. It essentially flushes the output buffer, ensuring that all pending output is written to the respective file stream. In this case, after each log entry was written using `fwrite()`, I would call `fflush()` to guarantee that the log was instantly accessible and up to date.

Here's a snippet illustrating its usage:

$logFile = 'chatlog.txt';
$logData = "User X sent a message: 'Hello, world!'";

$handle = fopen($logFile, 'a');
fwrite($handle, $logData . PHP_EOL);
fflush($handle); // Flushes the output buffer, making the log data immediately available

By incorporating `fflush()` after `fwrite()`, I managed to overcome the buffering issue and ensure real-time log updates. Just remember, as mentioned previously, depending on the frequency of writes and the size of the data, excessive use of `fflush()` might impact performance due to additional disk operations.

I hope this adds some value to your understanding of `fflush()` in PHP. Don't hesitate to reach out if you have any further questions!



Hey John,

I stumbled upon your query about the PHP `fflush()` function and thought I could share my experience with it. In my web scraping project, I encountered a situation where I needed immediate updates in the scraped data that was being written to a file.

Initially, I was using the `fwrite()` function to write the data, but I noticed there was a delay before the written content became visible in the file. This buffering behavior was not desirable as I wanted real-time access to the scraped data.

After some research, I found that using `fflush()` right after the `fwrite()` operation solved my problem. This function essentially flushes the output buffer, ensuring that all pending data is immediately written to the file.

Here's a snippet that demonstrates how I implemented it:

$filename = 'scraped_data.txt';
$data = "Scraped data: Lorem ipsum dolor sit amet.";

$handle = fopen($filename, 'w');
fwrite($handle, $data);
fflush($handle); // Flushes the output buffer, making the data instantly available in the file

By adding `fflush($handle)` after the `fwrite($handle, $data)` line, the scraped data was immediately saved to the file, giving me the real-time updates that I needed for further processing.

Keep in mind that it's important to use `fflush()` judiciously, as excessive use may impact performance due to increased disk I/O operations. It's best to utilize it only when immediate data visibility is crucial, like in real-time applications or scenarios where prompt access to the written content is required.

I hope this insight based on my personal experience helps you grasp the concept of the `fflush()` function better. Feel free to ask any more questions you may have!

Best regards,

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