Data storage functions play an extremely important role in PHP. There are a variety of data storage functions in PHP, including file operation functions, database operation functions, and so on. This article will focus on how to use data storage functions in PHP.

1. File operation function

1. fopen() function: Open the file and return the file pointer. The syntax is as follows:

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

   Among them, $filename is a required option, which refers to the file path to be opened; $mode is a required option, which specifies the file opening mode, such as "r" means read-only opening, "w" means only Write open etc.

2. fwrite() function: writes data to an opened file. The syntax is as follows:

   int fwrite ( resource $handle , string $string [, int $length ] )

   Among them, $handle is a required option and refers to the file pointer; $ string is a required option and refers to the string to be written; $length is optional and refers to the maximum number of bytes to be written.

3. fclose() function: close an open file. The syntax is as follows:

   bool fclose ( resource $handle )

   Among them, $handle is a required option and refers to the file pointer.

Sample code:

$file = fopen("test.txt","w");
fwrite($file,"Hello World. Testing!");
fclose($file);

The above code creates a file test.txt and writes the string "Hello World. Testing!" into it.

2. Database operation function

1. mysqli_connect() function: connect to the MySQL database, the syntax is as follows:

   mysqli mysqli_connect ( string $host = ini_get("mysqli.default_host") , string $username = ini_get("mysqli.default_user") , string $password = ini_get("mysqli.default_pw") , string $dbname = "" , int $port = ini_get("mysqli.default_port") , string $socket = ini_get("mysqli.default_socket") )

   Among them, $host is optional, Specify the address of the MySQL server to be connected; $username is optional and specifies the user name to connect to the MySQL server; $password is optional and specifies the password to connect to the MySQL server; $dbname is optional and specifies the name of the database to be connected; $port It is optional and specifies the MySQL server port number to be connected; $socket is optional and specifies the MySQL server socket to be used.

2. mysqli_query() function: execute a MySQL query statement, the syntax is as follows:

   mixed mysqli_query ( mysqli $link , string $query [, int $resultmode = MYSQLI_STORE_RESULT ] )

   Among them, $link is a required option, specifying the MySQL connection identifier; $query is Required option, specifies the MySQL query statement to be executed; $resultmode is optional, specifying the method of obtaining the result set. For example, MYSQLI_STORE_RESULT indicates that the result set is retained on the client side, MYSQLI_USE_RESULT indicates that the result set is retained on the server side, etc.

3. mysqli_fetch_array() function: Get a row from the result set as an associative array, a numeric array, or both. The syntax is as follows:

   mixed mysqli_fetch_array ( mysqli_result $result [, int $resulttype = MYSQLI_BOTH ] )

   Among them, $result is required Option, specifying the result set; $resulttype is optional, specifying the return array type, for example, MYSQLI_BOTH is the default value, indicating that associative arrays and numeric arrays are returned.

Sample code:

$link = mysqli_connect("localhost","my_user","my_password","my_db");
$result = mysqli_query($link,"SELECT * FROM user");
while($row = mysqli_fetch_array($result)) {
    echo $row['username'] . " - " . $row['email'];
    echo "<br>";
}
mysqli_close($link);

The above code connects to a MySQL database named "my_db", executes a SELECT statement to query all data in the user table, and Print the results line by line.

To sum up, there are many data storage functions in PHP, and file operation functions and database operation functions are the two most commonly used ones. Mastering their usage can enable more efficient data storage and management in actual development.

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