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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php把负数转为正整数的方法:1、使用abs()函数将负数转为正数,使用intval()函数对正数取整,转为正整数,语法“intval(abs($number))”;2、利用“~”位运算符将负数取反加一,语法“~$number + 1”。

实现方法:1、使用“sleep(延迟秒数)”语句,可延迟执行函数若干秒;2、使用“time_nanosleep(延迟秒数,延迟纳秒数)”语句,可延迟执行函数若干秒和纳秒;3、使用“time_sleep_until(time()+7)”语句。

php除以100保留两位小数的方法:1、利用“/”运算符进行除法运算,语法“数值 / 100”;2、使用“number_format(除法结果, 2)”或“sprintf("%.2f",除法结果)”语句进行四舍五入的处理值,并保留两位小数。

判断方法:1、使用“strtotime("年-月-日")”语句将给定的年月日转换为时间戳格式;2、用“date("z",时间戳)+1”语句计算指定时间戳是一年的第几天。date()返回的天数是从0开始计算的,因此真实天数需要在此基础上加1。

方法:1、用“str_replace(" ","其他字符",$str)”语句,可将nbsp符替换为其他字符;2、用“preg_replace("/(\s|\ \;||\xc2\xa0)/","其他字符",$str)”语句。

php判断有没有小数点的方法:1、使用“strpos(数字字符串,'.')”语法,如果返回小数点在字符串中第一次出现的位置,则有小数点;2、使用“strrpos(数字字符串,'.')”语句,如果返回小数点在字符串中最后一次出现的位置,则有。

php字符串有下标。在PHP中,下标不仅可以应用于数组和对象,还可应用于字符串,利用字符串的下标和中括号“[]”可以访问指定索引位置的字符,并对该字符进行读写,语法“字符串名[下标值]”;字符串的下标值(索引值)只能是整数类型,起始值为0。

查找方法:1、用strpos(),语法“strpos("字符串值","查找子串")+1”;2、用stripos(),语法“strpos("字符串值","查找子串")+1”。因为字符串是从0开始计数的,因此两个函数获取的位置需要进行加1处理。


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