get_option( string $option, mixed $default = false )

根据选项名称检索选项值。
Retrieves an option value based on an option name.

说明（Description）

如果选项不存在或没有值，则返回值将为false。这有助于检查是否需要安装一个选项，并且在安装插件选项时通常使用它，并测试是否需要升级。

如果该选项已序列化，则在返回时将其取消序列化。

任何标量值都将作为字符串返回。您可以通过注册“optionu$option”筛选器回调来强制给定选项的返回类型。

参数（Parameters）

返回（Return）

源码（Source）

/**
 * Retrieve option value based on name of option.
 *
 * If the option does not exist or does not have a value, then the return value
 * will be false. This is useful to check whether you need to install an option
 * and is commonly used during installation of plugin options and to test
 * whether upgrading is required.
 *
 * If the option was serialized then it will be unserialized when it is returned.
 *
 * @since 1.5.0
 *
 * @global wpdb $wpdb
 *
 * @param string $option  Name of option to retrieve. Expected to not be SQL-escaped.
 * @param mixed  $default Optional. Default value to return if the option does not exist.
 * @return mixed Value set for the option.
 */
function get_option( $option, $default = false ) {
	global $wpdb;

	$option = trim( $option );
	if ( empty( $option ) )
		return false;

	/**
	 * Filter the value of an existing option before it is retrieved.
	 *
	 * The dynamic portion of the hook name, `$option`, refers to the option name.
	 *
	 * Passing a truthy value to the filter will short-circuit retrieving
	 * the option value, returning the passed value instead.
	 *
	 * @since 1.5.0
	 *
	 * @param bool|mixed $pre_option Value to return instead of the option value.
	 *                               Default false to skip it.
	 */
	$pre = apply_filters( 'pre_option_' . $option, false );
	if ( false !== $pre )
		return $pre;

	if ( defined( 'WP_SETUP_CONFIG' ) )
		return false;

	if ( ! defined( 'WP_INSTALLING' ) ) {
		// prevent non-existent options from triggering multiple queries
		$notoptions = wp_cache_get( 'notoptions', 'options' );
		if ( isset( $notoptions[ $option ] ) ) {
			/**
			 * Filter the default value for an option.
			 *
			 * The dynamic portion of the hook name, `$option`, refers to the option name.
			 *
			 * @since 3.4.0
			 *
			 * @param mixed $default The default value to return if the option does not exist
			 *                       in the database.
			 */
			return apply_filters( 'default_option_' . $option, $default );
		}

		$alloptions = wp_load_alloptions();

		if ( isset( $alloptions[$option] ) ) {
			$value = $alloptions[$option];
		} else {
			$value = wp_cache_get( $option, 'options' );

			if ( false === $value ) {
				$row = $wpdb->get_row( $wpdb->prepare( "SELECT option_value FROM $wpdb->options WHERE option_name = %s LIMIT 1", $option ) );

				// Has to be get_row instead of get_var because of funkiness with 0, false, null values
				if ( is_object( $row ) ) {
					$value = $row->option_value;
					wp_cache_add( $option, $value, 'options' );
				} else { // option does not exist, so we must cache its non-existence
					if ( ! is_array( $notoptions ) ) {
						 $notoptions = array();
					}
					$notoptions[$option] = true;
					wp_cache_set( 'notoptions', $notoptions, 'options' );

					/** This filter is documented in wp-includes/option.php */
					return apply_filters( 'default_option_' . $option, $default );
				}
			}
		}
	} else {
		$suppress = $wpdb->suppress_errors();
		$row = $wpdb->get_row( $wpdb->prepare( "SELECT option_value FROM $wpdb->options WHERE option_name = %s LIMIT 1", $option ) );
		$wpdb->suppress_errors( $suppress );
		if ( is_object( $row ) ) {
			$value = $row->option_value;
		} else {
			/** This filter is documented in wp-includes/option.php */
			return apply_filters( 'default_option_' . $option, $default );
		}
	}

	// If home is not set use siteurl.
	if ( 'home' == $option && '' == $value )
		return get_option( 'siteurl' );

	if ( in_array( $option, array('siteurl', 'home', 'category_base', 'tag_base') ) )
		$value = untrailingslashit( $value );

	/**
	 * Filter the value of an existing option.
	 *
	 * The dynamic portion of the hook name, `$option`, refers to the option name.
	 *
	 * @since 1.5.0 As 'option_' . $setting
	 * @since 3.0.0
	 *
	 * @param mixed $value Value of the option. If stored serialized, it will be
	 *                     unserialized prior to being returned.
	 */
	return apply_filters( 'option_' . $option, maybe_unserialize( $value ) );
}

笔记（Notes）