fgets

(PHP 4, PHP 5, PHP 7, PHP 8)

fgets — 从文件指针中读取一行

说明

fgets(resource $stream, ?int $length = null): string|false

从文件指针中读取一行。

参数

stream: 文件指针必须是有效的，必须指向由 fopen() 或 fsockopen() 成功打开的文件(并还未由 fclose() 关闭)。
length: 从 handle 指向的文件中读取一行并返回长度最多为 length - 1 字节的字符串。碰到换行符（包括在返回值中）、EOF 或者已经读取了 length - 1 字节后停止（看先碰到那一种情况）。如果没有指定 length，则默认为 1K，或者说 1024 字节。

返回值

从指针 stream 指向的文件中读取了 length - 1 字节后返回字符串。如果文件指针中没有更多的数据了则返回 false。

错误发生时返回 false。

示例

示例 #1 逐行读取文件

<?php

$fp = @fopen("/tmp/inputfile.txt", "r");

if ($fp) {
    while (($buffer = fgets($fp, 4096)) !== false) {
        echo $buffer, PHP_EOL;
    }

    if (!feof($fp)) {
        echo "Error: unexpected fgets() fail\n";
    }

fclose($fp);
}

?>

注释

注意: 在读取在 Macintosh 电脑中或由其创建的文件时，如果 PHP 不能正确的识别行结束符，启用运行时配置可选项 auto_detect_line_endings 也许可以解决此问题。

注意:
习惯了 C 语言中 fgets() 语法的人应该注意到 EOF 是怎样被返回的。

参见

fgetss() - 从文件指针中读取一行并过滤掉 HTML 标记
fread() - 读取文件（可安全用于二进制文件）
fgetc() - 从文件指针中读取字符
stream_get_line() - 从资源流里读取一行直到给定的定界符
fopen() - 打开文件或者 URL
popen() - 打开进程文件指针
fsockopen() - 打开 Internet 或者 Unix 套接字连接
stream_set_timeout() - Set timeout period on a stream

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用户贡献的备注 5 notes

down

Leigh Purdie ¶

9 years ago

A better example, to illustrate the differences in speed for large files, between fgets and stream_get_line.

This example simulates situations where you are reading potentially very long lines, of an uncertain length (but with a maximum buffer size), from an input source.

As Dade pointed out, the previous example I provided was much to easy to pick apart, and did not adequately highlight the issue I was trying to address.

Note that specifying a definitive end-character for fgets (ie: newline), generally decreases the speed difference reasonably significantly. 

#!/usr/bin/php
<?php
        $plaintext=file_get_contents('http://loripsum.net/api/60/verylong/plaintext');  # Should be around 90k characters
$plaintext=str_replace("\n"," ",$plaintext); # Get rid of newlines

$fp=fopen("/tmp/SourceFile.txt","w");
        for($i=0;$i<100000;$i++) {
fputs($fp,substr($plaintext,0,rand(4096,65534)) . "\n");
        }
fclose($fp);

$fp=fopen("/tmp/SourceFile.txt","r");
$start=microtime(true);
        while($line=fgets($fp,65535)) {
1;
        }
$end=microtime(true);
fclose($fp);
$delta1=($end - $start);

$fp=fopen("/tmp/SourceFile.txt","r");
$start=microtime(true);
        while($line=stream_get_line($fp,65535)) {
1;
        }
$end=microtime(true);
fclose($fp);
$delta2=($end - $start);

$pdiff=$delta1/$delta2;
        print "stream_get_line is " . ($pdiff>1?"faster":"slower") . " than fgets - pdiff is $pdiff\n";
?>

$ ./testcase.php 
stream_get_line is faster than fgets - pdiff is 1.760398041785

Note that, in a vast majority of situations in which php is employed, tiny differences in speed between system calls are of negligible importance.

down

Anonymous ¶

4 years ago

if you for some reason need to get lines from a string instead of a file pointer, try

<?php
function string_gets(string $source, int $offset = 0, string $delimiter = "\n"): ?string
{
$len = strlen($source);
    if ($len < $offset) {
// out of bounds.. maybe i should throw an exception
return null;
    }
    if ($len === $offset) {
// end of string..
return null;
    }
$delimiter_pos = strpos($source, $delimiter, $offset);
    if ($delimiter_pos === false) {
// last line.
return substr($source, $offset);
    }
    return substr($source, $offset, ($delimiter_pos - $offset) + strlen($delimiter));
}

?>

(i had a ~16GB string in-memory i needed to process line-by-line, but i would get memory-allocation-crash (on a 32GB ram system) if i tried explode("\n",$str); , so came up with this.. interestingly, fgets() seems to be faster than doing it in-ram-in-php, though. php 7.3.7)

down

David at Weintraub.name ¶

17 years ago

There's an error in the documentation:

The file pointer must be valid, and must point to a file successfully opened by fopen() or fsockopen() (and not yet closed by fclose()).

You should also add "popen" and "pclose" to the documentation. I'm a new PHP developer and went to verify that I could use "fgets" on commands that I used with "popen".

down

Peter Schlaile ¶

17 years ago

fscanf($file, "%s\n") isn't really a good substitution for fgets(), since it will stop parsing at the first whitespace and not at the end of line!

(See the fscanf page for details on this)

down

tavernadelleidee[italy] ¶

18 years ago

I think that the quickest way of read a (long) file with the rows in  reverse order is

<?php
$myfile = 'myfile.txt';
$command = "tac $myfile > /tmp/myfilereversed.txt";
passthru($command);
$ic = 0;
$ic_max = 100;  // stops after this number of rows
$handle = fopen("/tmp/myfilereversed.txt", "r");
while (!feof($handle) && ++$ic<=$ic_max) {
$buffer = fgets($handle, 4096);
   echo $buffer."<br>";
}
fclose($handle);
?>

It echos the rows while it is reading the file so it is good for long files like logs.

Borgonovo