


Recommended efficient methods for reading N lines at the end of large files in PHP.
Small files within a few megabytes can be read into an array line by line through the file() function. , and then use array_pop to get the last row.
But for very large text files, the machine memory is not large enough, or PHP itself has a memory_limit limit, so this method is not applicable. Even if there is no limit, the efficiency is very low.
Is there no other way? Of course there is, but there is no ready-made function, so you need to do it yourself.
A file pointer needs to be used here. Those who have studied C should know what a pointer is. To put it simply, in PHP, a file is opened through fopen. At this time, the file has not been read. At this time, it points to the beginning of the file. , the pointer position is 0. When you read content from a file through fgets or fgetc, the pointer will advance accordingly as you read. This is also
while(!feof($fp)){ $data.=fgets($fp,4096); }
The principle of implementation is that fgets reads a string of specified length backward from the current pointer position until a newline character is encountered.
So is it possible to control the position of the pointer to the Nth line from the bottom? Unfortunately, no, but you can move the pointer directly to the end and back N positions through the fseek() function.
We first move the pointer to the end and go back 2 positions, read a character through fgetc, and determine whether the character is "n", which is a newline character. If it is not a newline character, then continue to go back one position again. Judgment, until we go back to the ending newline character of the previous line, just use fgets to take out the entire line. Two while loops are used here. The outer loop controls the number of rows to be obtained, and the inner loop controls the fseek action.
The function is as follows:
/** * 取文件最后$n行 * @param string $filename 文件路径 * @param int $n 最后几行 * @return mixed false表示有错误,成功则返回字符串 */ function FileLastLines($filename,$n){ if(!$fp=fopen($filename,'r')){ echo "打开文件失败,请检查文件路径是否正确,路径和文件名不要包含中文"; return false; } $pos=-2; $eof=""; $str=""; while($n>0){ while($eof!="\n"){ if(!fseek($fp,$pos,SEEK_END)){ $eof=fgetc($fp); $pos--; }else{ break; } } $str.=fgets($fp); $eof=""; $n--; } return $str; } echo nl2br(FileLastLines('sss.txt',4));
The above recommendation for an efficient method for reading N lines at the end of a large file in PHP is all the content shared by the editor. I hope it can give you a reference, and I hope you will support Bangkejia more.

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。

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。

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。

在PHP中,可以利用implode()函数的第一个参数来设置没有分隔符,该函数的第一个参数用于规定数组元素之间放置的内容,默认是空字符串,也可将第一个参数设置为空,语法为“implode(数组)”或者“implode("",数组)”。

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。


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