How to determine whether a remote image file exists in PHP_PHP Tutorial

fopen() method

The easiest way is to use fopen() to see if the file can be opened. If it can be opened, the file will of course exist.

<?php
$url = 'http://www.bkjia.com/images/test.jpg';

if( @fopen( $url, 'r' ) ) 
{ 
	echo 'File Exits';
} 
else 
{
	echo 'File Do Not Exits';
}
?>

fopen() function opens a file or URL. If the open fails, the function returns FALSE.

Syntax: fopen(filename,mode,include_path,context)

参数	描述
filename	必需。规定要打开的文件或 URL。
mode	必需。规定要求到该文件/流的访问类型。可能的值见下表。
include_path	可选。如果也需要在 include_path 中检索文件的话，可以将该参数设为 1 或 TRUE。
context	可选。规定文件句柄的环境。Context 是可以修改流的行为的一套选项。

Possible values ​​for the mode parameter:

mode	说明
"r"	只读方式打开，将文件指针指向文件头。
"r+"	读写方式打开，将文件指针指向文件头。
"w"	写入方式打开，将文件指针指向文件头并将文件大小截为零。如果文件不存在则尝试创建之。
"w+"	读写方式打开，将文件指针指向文件头并将文件大小截为零。如果文件不存在则尝试创建之。
"a"	写入方式打开，将文件指针指向文件末尾。如果文件不存在则尝试创建之。
"a+"	读写方式打开，将文件指针指向文件末尾。如果文件不存在则尝试创建之。
"x"	创建并以写入方式打开，将文件指针指向文件头。如果文件已存在，则 fopen() 调用失败并返回 FALSE，并生成一条 E_WARNING 级别的错误信息。如果文件不存在则尝试创建之。这和给底层的 open(2) 系统调用指定 O_EXCL|O_CREAT 标记是等价的。此选项被 PHP 4.3.2 以及以后的版本所支持，仅能用于本地文件。
"x+"	创建并以读写方式打开，将文件指针指向文件头。如果文件已存在，则 fopen() 调用失败并返回 FALSE，并生成一条 E_WARNING 级别的错误信息。如果文件不存在则尝试创建之。这和给底层的 open(2) 系统调用指定 O_EXCL|O_CREAT 标记是等价的。此选项被 PHP 4.3.2 以及以后的版本所支持，仅能用于本地文件。

fopen() binds the name resource specified by filename to a stream. If filename is of the form "scheme://...", it is treated as a URL and PHP will search for a protocol handler (also called a wrapper protocol) to handle the scheme. If the wrapper protocol has not been registered for the protocol, PHP will emit a message to help check for potential problems in the script and continue execution of filename as if it were a normal filename.

If PHP thinks filename specifies a local file, it will try to open a stream on that file. The file must be accessible to PHP, so you need to confirm that the file access permissions allow this access. If safe mode or open_basedir is activated further restrictions apply.

If PHP believes that filename specifies a registered protocol, and the protocol is registered as a network URL, PHP will check and confirm that allow_url_fopen has been activated. If it is closed, PHP will issue a warning and the call to fopen will fail.

Usage of fopen

<?php
$file = fopen("test.txt","r");
$file = fopen("/home/test/test.txt","r");
$file = fopen("/home/test/test.gif","wb");
$file = fopen("http://www.example.com/","r");
$file = fopen("ftp://user:password@example.com/test.txt","w");
?>

But if the server where the image resource is located hangs up, this function will wait forever, so we need a backup plan.

CURL method

CURL is a very useful class library. Let’s see how to use it to judge.

<?php
$url2 = 'http://www.bkjia.com/test.jpg';

$ch = curl_init(); 
$timeout = 10; 
curl_setopt ($ch, CURLOPT_URL, $url2); 
curl_setopt($ch, CURLOPT_HEADER, 1); 
curl_setopt ($ch, CURLOPT_RETURNTRANSFER, 1); 
curl_setopt ($ch, CURLOPT_CONNECTTIMEOUT, $timeout); 

$contents = curl_exec($ch);
//echo $contents;
if (preg_match("/404/", $contents)){
	echo '文件不存在';
}
?>

If the file does not exist after curl_exec() is executed, the following information will be returned:

HTTP/1.1 404 Not Found
Date: Tue, 14 Feb 2012 05:08:34 GMT
Server: Apache
Accept-Ranges: bytes
Content-Length: 354
Content-Type: text/html

Use regular expressions to see if there is a 404. If so, the file does not exist.

http://www.bkjia.com/PHPjc/752418.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/752418.htmlTechArticlefopen() method The simplest method is to use fopen() to see if the file can be opened. If it can be opened, Of course the file exists. ?php$url = 'http://www.bkjia.com/images/test.jpg';if( @fopen( $url,...