Current Location: Home> Latest Articles> How to use vfprintf and fwrite to achieve flexible format output

How to use vfprintf and fwrite to achieve flexible format output

gitbox 2025-05-27

fwrite: Basic binary output function

fwrite is a function for writing data to a file. Its basic usage is as follows:

 $fp = fopen('log.txt', 'w');
fwrite($fp, "Logging begins\n");
fclose($fp);

In this example, we open a file called log.txt and write a line of text to it. If the file does not exist, fopen will automatically create it.

Although fwrite is very direct, when writing structured or formatted data, it is not elegant to splice strings alone, and the code is not easy to maintain.

vfprintf: A powerful tool for formatting output

vfprintf is a variant of fprintf that allows us to output using format control characters and parameter arrays. This is great for dynamically generating formatted strings. For example:

 $fp = fopen('report.txt', 'w');
$data = ['John Doe', 28, 3.75];
vfprintf($fp, "Name: %s, age: %d, score: %.2f\n", $data);
fclose($fp);

The output will be:

 Name: John Doe, age: 28, score: 3.75

The benefits of this approach are:

  • Maintain consistency of the output structure

  • Easy to batch generate content based on format templates

  • Format control characters are safer and clearer than string stitching

Practical combat: Combining fwrite and vfprintf

In actual development, we usually use fwrite with vfprintf to implement conditional control or more complex logic.

For example, suppose we want to write a set of user activity records, and the record also contains access links:

 $fp = fopen('activity.log', 'a');

$users = [
    ['Alice', 'login', 'https://gitbox.net/user/alice'],
    ['Bob', 'upload', 'https://gitbox.net/files/12345'],
    ['Charlie', 'download', 'https://gitbox.net/files/67890']
];

foreach ($users as $entry) {
    list($name, $action, $url) = $entry;
    $line = sprintf("[%s] user %s Performed: %s，Details: %s\n", date('Y-m-d H:i:s'), $name, $action, $url);
    fwrite($fp, $line);
}

fclose($fp);

Example of output content:

 [2025-05-27 13:45:02] user Alice Performed: login，Details: https://gitbox.net/user/alice
[2025-05-27 13:45:02] user Bob Performed: upload，Details: https://gitbox.net/files/12345
[2025-05-27 13:45:02] user Charlie Performed: download，Details: https://gitbox.net/files/67890

Tips and precautions for use

  1. Resource management : Always use fclose() to close open file pointers to avoid resource leakage.

  2. Format control : Try to use %s , %d , %f and other control characters instead of string splicing, which is safer and more reliable.

  3. Path security : When involving URLs, ensure that the domain names and parameters in the path are controllable, such as https://gitbox.net .

  4. Write performance : For large numbers of write operations, consider buffering writes or using ob_start() to cache the output and write files uniformly.

Related