Can php clear file contents?

php can clear the file contents. The implementation method is: first create a PHP sample file; then open the file through "fopen($path, "r ");"; finally through "if( flock($fh , LOCK_EX) ){...}" to clear the file contents.

The operating environment of this article: windows7 system, PHP7.1 version, DELL G3 computer

Specific questions:

php clear file contents?

How to clear the contents of a file in php without using fopen($file, 'w ').

My requirement is this. I want to ensure that all the last content after writing the file is deleted. If I overwrite it directly, it will only cover the content I wrote this time. If the old content is longer than the new content, then it will The rest, and the PHP program needs to run 24 hours a day, and the operating efficiency must be ensured. I tried the fopen() method, and found that a lot of time was wasted when closing and opening file resources. I tested turning on the file lock on my local machine. Every time you use fopen() to clear a file, it can only be executed 5,000 times per second. If you only read and write, it can be executed nearly 200,000 times per second, so I would like to ask if there are other methods. achieve this purpose.

The implementation code is as follows:

$fh = fopen($path, "r+");
if( flock($fh, LOCK_EX) ){//加写锁
$old_content=json_decode(fread($fh,filesize($path)),true);
$old_content=$old_content.$new_content;
ftruncate($fh,0); // 将文件截断到给定的长度
rewind($fh); // 倒回文件指针的位置
fwrite($fh,json_encode($old_content));
// @chmod($path,0644);
flock($fh, LOCK_UN); //解锁
}
fclose($fh);

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