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Top Forums Programming C++ class definition with a member of the same class Post 302430729 by Corona688 on Friday 18th of June 2010 01:15:48 PM
Old 06-18-2010
Quote:
Originally Posted by pogdorica
Hi, i have a question about C++. Is it possible to declare a class with a member ot the same class?
I don't think you can. Think about it: Wouldn't that class inside the class, also have a class inside the class? Which would also have a class inside the class. etc. etc. etc. If you want different things to have different members, they have to be different structures.

This doesn't even work in C. Observe:
Code:
typedef struct whatever
{
    int a;
    struct whatever s;
} whatever;

will give an error since you can't nest that way.

You can cheat by using a pointer. The compiler will let you make pointers to incomplete types since a pointer's always the same size.

Code:
typedef struct linkedlist
{
    int payload;
    struct linkedlist *next;
} linkedlist;

That way it only allocates the size of the pointer, not the entire struct, avoiding the infinite recursion. This means you have to explicitly allocate memory to it later to use it, of course.
 

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STRUCT 
CLASS(9) Device drivers infrastructure STRUCT CLASS(9) NAME
struct_class - device classes SYNOPSIS
struct class { const char * name; struct module * owner; struct class_attribute * class_attrs; struct device_attribute * dev_attrs; const struct attribute_group ** dev_groups; struct bin_attribute * dev_bin_attrs; struct kobject * dev_kobj; int (* dev_uevent) (struct device *dev, struct kobj_uevent_env *env); char *(* devnode) (struct device *dev, umode_t *mode); void (* class_release) (struct class *class); void (* dev_release) (struct device *dev); int (* suspend) (struct device *dev, pm_message_t state); int (* resume) (struct device *dev); const struct kobj_ns_type_operations * ns_type; const void *(* namespace) (struct device *dev); const struct dev_pm_ops * pm; struct subsys_private * p; }; MEMBERS
name Name of the class. owner The module owner. class_attrs Default attributes of this class. dev_attrs Default attributes of the devices belong to the class. dev_groups Default attributes of the devices that belong to the class. dev_bin_attrs Default binary attributes of the devices belong to the class. dev_kobj The kobject that represents this class and links it into the hierarchy. dev_uevent Called when a device is added, removed from this class, or a few other things that generate uevents to add the environment variables. devnode Callback to provide the devtmpfs. class_release Called to release this class. dev_release Called to release the device. suspend Used to put the device to sleep mode, usually to a low power state. resume Used to bring the device from the sleep mode. ns_type Callbacks so sysfs can detemine namespaces. namespace Namespace of the device belongs to this class. pm The default device power management operations of this class. p The private data of the driver core, no one other than the driver core can touch this. DESCRIPTION
A class is a higher-level view of a device that abstracts out low-level implementation details. Drivers may see a SCSI disk or an ATA disk, but, at the class level, they are all simply disks. Classes allow user space to work with devices based on what they do, rather than how they are connected or how they work. COPYRIGHT
Kernel Hackers Manual 3.10 June 2014 STRUCT CLASS(9)
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