How do PHP functions return resources?

PHP functions allocate system resources (database connections, file handles, etc.) through built-in functions to return resource handles: 1. fopen - file processing; 2. fsockopen - network connection; 3. mysqli_connect - database connection; 4. curl_init - HTTP ask. Be sure to close resources properly to free up system resources.

How do PHP functions return resources?

Resource Type

In PHP, a resource is a special data type that represents a system or external resource, such as a file, network connection, or database link. Resources are typically created and managed by built-in functions.

Functions that return resources

There are several functions in PHP that can return resources:

• fopen():Open the file and return the file handle.
• fsockopen(): Establishes a network socket connection and returns the socket handle.
• mysqli_connect(): Connect to the MySQL database and return the database connection handle.
• curl_init(): Initialize a cURL session for making HTTP requests and return the resource handle.

Practical case: Open a file

Let us use the fopen() function to open a file and return the file handle:

<?php

// 打开文件并获取文件句柄
$fileHandle = fopen("test.txt", "r");

// 检查是否成功打开文件
if ($fileHandle) {
    // 使用文件句柄读取文件内容
    $fileContents = fread($fileHandle, filesize("test.txt"));

    // 关闭文件
    fclose($fileHandle);
} else {
    // 打开文件失败
    echo "无法打开文件！";
}

?>

Notes on returning resources

• Resources need to be closed in time to release system resources.
• Most PHP functions require resources as parameters and will automatically close them.
• Do not pass the resource handle directly to functions such as var_dump() or print_r(), otherwise it will cause unexpected output results.

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