Instructions for using fopen function to open files in php

1.resource fopen(string $filename, string $mode [,bool $use_include_path [, resource $zcontext]])
Function function:
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 protocol has not been registered as a wrapper protocol, PHP will emit a message to help check for potential problems in the script and continue execution of filename as 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 thinks 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.

filename: Specifies the file or URL to be opened.
mode: Specifies the type of access required to the file/stream.
include_path: Optional, if you also need to retrieve files in include_path, you can set this parameter to 1 or TRUE.
context: Optional, specifies the environment of the file handle. Context is a set of options that can modify the behavior of the stream.

Possible values ​​​​of the mode parameter
mode Description
"r" Open in read-only mode, pointing the file pointer to the file header.
"r+" Open in reading and writing mode and point the file pointer to the file header.
"w" Open in writing mode, point the file pointer to the file header and truncate the file size to zero. If the file does not exist, try to create it.
"w+" Open in reading and writing mode, point the file pointer to the file header and cut the file size to zero. If the file does not exist, try to create it.
"a" Open in writing mode and point the file pointer to the end of the file. If the file does not exist, try to create it.
"a+" Open in read-write mode and point the file pointer to the end of the file. If the file does not exist, try to create it.
"x"
Create and open for writing, pointing the file pointer to the file header. If the file already exists, the fopen() call fails and returns FALSE and generates an E_WARNING level error message. If the file does not exist, try to create it.
This is equivalent to specifying the O_EXCL|O_CREAT flag to the underlying open(2) system call.
This option is supported by PHP 4.3.2 and later versions and can only be used for local files.

"x+"
Create and open in read-write mode, pointing the file pointer to the file header. If the file already exists, the fopen() call fails and returns FALSE and generates an E_WARNING level error message. If the file does not exist, try to create it.
This is equivalent to specifying the O_EXCL|O_CREAT flag to the underlying open(2) system call.
This option is supported by PHP 4.3.2 and later versions and can only be used for local files.

Note:
Different operating system families have different line ending habits. When writing to a text file and want to insert a new line, you need to use operating system-compliant line endings. Unix-based systems use n as the line-ending character, Windows-based systems use rn as the line-ending character, and Macintosh-based systems use r as the line-ending character.

If you write files with the wrong line endings, other applications may behave strangely when opening those files.
Windows provides a text conversion tag ('t') to transparently convert n to rn. Alternatively, 'b' can be used to force binary mode so that the data is not converted. To use these flags, use either 'b' or 't' as the last character of the mode argument.

The default conversion mode depends on the SAPI and PHP version used, so for portability it is encouraged to always specify the appropriate tags. If you are working with plain text files and using n as the line terminator in your script, but you also want the files to be readable by other applications such as Notepad, use 't' in mode. Use 'b' in all other cases.

If you do not specify the 'b' flag when operating binary files, you may encounter some strange problems, including corrupted image files and strange issues with the rn character.

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