What to do if php cannot read the file

Solution to the problem that php cannot read the file: 1. Use the function [fread()] to return the read string, and return FALSE if an error occurs; 2. Use the function [fgets()] to point to the string from the handle Read a line from the file and return a string with a length of at most [length - 1] bytes.

Solution to php unable to read the file:

1.fread

string fread ( int $handle , int $length )

fread() Reads up to length bytes from the file pointed to by handle. This function is called after reading up to length bytes, or when EOF is reached, or (for network streams) when a packet is available, or (after opening a user space stream) 8192 bytes have been read. Will stop reading the file, depending on which condition is encountered first.

fread() returns the read string, and returns FALSE if an error occurs.

<?php
    $filename = "/usr/local/something.txt";
    $handle = fopen($filename, "r");//读取二进制文件时，需要将第二个参数设置成&#39;rb&#39;
    
    //通过filesize获得文件大小，将整个文件一下子读到一个字符串中
    $contents = fread($handle, filesize ($filename));
    fclose($handle);
?>

If the file to be read is not a local ordinary file, but a remote file or stream file, this method cannot be used because filesize cannot obtain the size of these files. At this time, you need to use the return value of feof() or fread() to determine whether the end of the file has been read.

For example:

<?php
    $handle = fopen(&#39;http://www.baidu.com&#39;, &#39;r&#39;);
    $content = &#39;&#39;;
    while(!feof($handle)){
        $content .= fread($handle, 8080);
    }
    echo $content;
    fclose($handle);
?>

or:

<?php
    $handle = fopen(&#39;http://www.baidu.com&#39;, &#39;r&#39;);
    $content = &#39;&#39;;
    while(false != ($a = fread($handle, 8080))){//返回false表示已经读取到文件末尾
        $content .= $a;
    }
    echo $content;
    fclose($handle);
?>

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2.fgets

string fgets ( int $handle [, int $length ] )

fgets() reads a line from the file pointed to by handle And returns a string with a length of at most length - 1 bytes. Stops when a newline character (included in the return value), EOF, or length - 1 bytes has been read (whichever occurs first). If length is not specified, it defaults to 1K, or 1024 bytes.

<?php
    $handle = fopen(&#39;./file.txt&#39;, &#39;r&#39;);
    while(!feof($handle)){
        echo fgets($handle, 1024);
    }
    fclose($handle);
?>

Note: The length parameter becomes optional as of PHP 4.2.0. If omitted, the length of the line is assumed to be 1024. Starting with PHP 4.3, omitting length will continue reading from the stream until the end of the line. If most of the lines in the file are larger than 8KB, specifying the maximum line length in the script is more efficient in utilizing resources. Starting with PHP 4.3 this function is safe for use with binary files. Earlier versions don't.

3.fgetss

string fgetss ( resource $handle [, int $length [, string $allowable_tags ]] )

The same function as fgets, but fgetss will try to remove any HTML and PHP tags from the read text, you can use the optional first Three parameters specify which tags are not to be removed.

<?php
    $handle = fopen(&#39;./file.txt&#39;, &#39;r&#39;);
    while(!feof($handle)){
        echo fgetss($handle, 1024, &#39;<br>&#39;);
    }
    fclose($handle);
?>

4.file

array file ( string $filename [, int $use_include_path [, resource $context ]] )

Read the file contents into an array. Each item in the array corresponds to a line in the file, including newlines. You can use the rtrim() function to filter out newline characters when line terminators are not required.

<?php
    $a = file(&#39;./file.txt&#39;);
    foreach($a as $line => $content){
        echo &#39;line &#39;.($line + 1).&#39;:&#39;.$content;
    }
?>

5.readfile

int readfile ( string $filename [, bool $use_include_path [, resource $context ]] )

Read a file and write it to the output buffer. Returns the number of bytes read from the file. Returns FALSE on error and displays an error message unless called as @readfile().

<?php
    $size = readfile(&#39;./file.txt&#39;);
    echo $size;
?>

6.file_get_contents

string file_get_contents ( string $filename [, bool $use_include_path [, resource $context [, int $offset [, int $maxlen ]]]] )

Read the file into a string. The third parameter $context can be used to set some parameters, such as setting timeout when accessing remote files, etc.

In addition, file_get_contents has much better performance than the above functions, so file_get_contents should be given priority. But readfile seems to have better performance than file_get_contents (?), because it does not need to call fopen.

<?php 
    $ctx = stream_context_create(array( 
        &#39;http&#39; => array( 
            &#39;timeout&#39; => 1    //设置超时
            ) 
        ) 
    ); 
    echo file_get_contents("http://www.baidu.com/", 0, $ctx); 
?>

7.fpassthru

int fpassthru ( resource $handle )

Reads the given file pointer from the current position to EOF and writes the result to the output buffer.

<?php 
    header("Content-Type:text/html;charset=utf-8"); 
    $handle = fopen(&#39;./test2.php&#39;, &#39;r&#39;);
    fseek($handle, 1024);//将指针定位到1024字节处
    fpassthru($handle);
?>

A few notes:

1. It is encouraged to use the b flag when processing binary files, even if the system does not require it, which can make the script more portable.

2. The allow_url_fopen option activates the URL form of the fopen encapsulation protocol so that URL objects such as files can be accessed. The default encapsulation protocol provides access to remote files using the ftp and http protocols. Some extension libraries such as zlib may register more encapsulation protocols. For security reasons, this option can only be set in php.ini.

3. If you want to open a URL with special characters (for example, spaces), you need to use urlencode() for URL encoding.

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