PHP 打开文件

Modern software solutions require interactions with files. They may require to accept inputs from files or either write output and add it to the file. In either situation, the capability of integrating with files has become an important feature for almost all software that is used to run businesses. In this topic, we are going to learn about PHP Open File. In this tutorial, we will be learning about Php functions that allow us to open files located locally or hosted on a Url and use the file and its content for different purposes.

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The fopen Php function

The fopen Php function is an in-built function and is used to open files for different purposes in Php.

The syntax of fopen is as below:

fopen ( $filename ,  $mode [$use_include_path = FALSE [,  $context ]] )

In the above syntax,

$filename stands for the name of the file we’d like to open. This could be either a file locally stored or a file hosted on a different server and can be accessed. If the filename is in the form of a Url, then Php will first search for the protocol handler (also known as a wrapper) for that particular protocol. In case if no wrapper is found, Php will then return an error.

If the filename protocol has a registered wrapper, Php will then check if allow_url_fopen is disabled or enabled. If enabled, the fopen will be executed else it will fail with an error message returned.

If a local filename is supplied as $filename, in that case, Php will open a stream to that file. That’s why it’s important to make sure that the file is accessible to Php and the right access is set for the file. You should make sure that safe mode or open_basedir are not activated else further restrictions may apply to access the file.

The syntax for the fopen() Php function is as follows:

<?php
$myFileHandle = fopen("c:\folder\resource.txt", "r");
?>

However, when using a Windows operating system we need to escape any backslashes used in file location or use forward slashes instead.

So the above syntax, when written for a Windows OS, changes to:

<?php
$myFileHandle = fopen("c:\\folder\\resource.txt", "r");
?>

The Mode parameter in fopen()

The mode parameter in fopen() indicates the access level with which the file should be opened. The following different accesses and options are available in php and can be passed as a value for mode:

1. r: The option “r” is used to open the file is the only read-only mode. It places the file pointer at the start of the file for the purpose of reading.
2. r+: The option “r+” is used to open the file for both reading and writing purpose. It places the file pointer at the start of the file.
3. w: It opens the file for writing only. It also places the pointer at the start of the file and truncates the file length to 0. In case if the file doesn’t exist, it will create a new file.
4. w+: It is used to open the file for both reading and writing purpose. It also places the pointer at the start of the file and truncates the file length to 0. In case if the file doesn’t exist, it will create a new file in the provided location.
5.  a: It opens the file in write-only mode and places the file pointer to the end. In case if the file is not present, it will create the file with the provided filename.
6. a+: It opens the file for reading and writing both and places the file pointer to the end. In case if the file is not present, it will create the file with the provided filename.
7. x: It creates a file for writing purposes only and places the file pointer at the beginning of the file. If the file is already present at the location, fopen() will fail and will return a false value generating an error. If the file does not exist, the fopen function will create it.
8. x+: It creates a file for both writing as well as reading and places the file pointer at the beginning of the file. If the file is already present at the location, fopen() will fail and will return a false value generating an error. If the file does not exist, the fopen function will create it.
9.  c: It opens the file in write-only mode. If the file doesn’t exist at the provided location, it will attempt to create one. In case if the file exists, it doesn’t truncate it as compared to “w”. However, it does position the file pointer to the start of the file.
10. c+: It opens the file for writing and reading mode. If the file doesn’t exist at the provided location, it will attempt to create one. In case if the file exists, it doesn’t truncate it as compared to “w”. However, it does position the file pointer to the start of the file.

Use_include_path parameter

It is an optional input parameter in the fopen() function. It accepts values in Boolean. If provided true, it searched the provided filename in the paths included using include_path too.

The fopen() function returns a file pointer when the file is accessed successfully else will return a False value on failure.

Let’s review a few examples below:

Example #1 – read a file

Let’s create a file with the content “My fopen with read mode example” and place it in the Php ecosystem.

With the below code, let’s attempt to open read the file content.

Code:

<?php
$my_file = fopen("demo.txt", "r") or die("Unable to open file!");
echo fread($my_file,filesize("demo.txt"));
fclose($my_file);
?>

Output:

Example #2 – write to a file

Let’s create and write a file in php with the following example:

Code:

<?php
$myfile = fopen("my_file.txt", "a") or die("Unable to open file!");
$txt = "I know how to write to a file now";
fwrite($my_file, $txt);
$myfile = fopen("my_file.txt", "r") or die("Unable to open file!");
echo fread($my_file,filesize($myfile));
fclose($myfile);
?>

Output:

The above code would also have created a file with the name ”my_file.txt”.

Example #3 – append to a file:

Code:

<?php
$myfile = fopen("my_file.txt", "w") or die("Unable to open file!");
$txt = "I have now added a 2nd line";
fwrite($my_file, $txt);
$myfile = fopen("my_file.txt", "w") or die("Unable to open file!");
echo "I know how to write to a file now";
fclose($myfile);
?>

Output:

Conclusion – PHP Open File

With the above explanation and examples, we can conclude that fopen() can be used for a variety of reading, writing, and appending options. It can be used to operate with the file on the same server as well as a different server.

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