вставить или удалить элемент в очереди (insert or remove an element in a queue)
Пролог (Prolog)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
Имя (Name)
insque, remque — insert or remove an element in a queue
Синопсис (Synopsis)
#include <search.h>
void insque(void *element, void *pred);
void remque(void *element);
Описание (Description)
The insque() and remque() functions shall manipulate queues built
from doubly-linked lists. The queue can be either circular or
linear. An application using insque() or remque() shall ensure it
defines a structure in which the first two members of the
structure are pointers to the same type of structure, and any
further members are application-specific. The first member of the
structure is a forward pointer to the next entry in the queue.
The second member is a backward pointer to the previous entry in
the queue. If the queue is linear, the queue is terminated with
null pointers. The names of the structure and of the pointer
members are not subject to any special restriction.
The insque() function shall insert the element pointed to by
element into a queue immediately after the element pointed to by
pred.
The remque() function shall remove the element pointed to by
element from a queue.
If the queue is to be used as a linear list, invoking
insque(&element, NULL), where element is the initial element of
the queue, shall initialize the forward and backward pointers of
element to null pointers.
If the queue is to be used as a circular list, the application
shall ensure it initializes the forward pointer and the backward
pointer of the initial element of the queue to the element's own
address.
Возвращаемое значение (Return value)
The insque() and remque() functions do not return a value.
Ошибки (Error)
No errors are defined.
The following sections are informative.
Примеры (Examples)
Creating a Linear Linked List
The following example creates a linear linked list.
#include <search.h>
...
struct myque element1;
struct myque element2;
char *data1 = "DATA1";
char *data2 = "DATA2";
...
element1.data = data1;
element2.data = data2;
insque (&element1, NULL);
insque (&element2, &element1);
Creating a Circular Linked List
The following example creates a circular linked list.
#include <search.h>
...
struct myque element1;
struct myque element2;
char *data1 = "DATA1";
char *data2 = "DATA2";
...
element1.data = data1;
element2.data = data2;
element1.fwd = &element1;
element1.bck = &element1;
insque (&element2, &element1);
Removing an Element
The following example removes the element pointed to by element1.
#include <search.h>
...
struct myque element1;
...
remque (&element1);
Использование в приложениях (Application usage)
The historical implementations of these functions described the
arguments as being of type struct qelem * rather than as being of
type void * as defined here. In those implementations, struct
qelem was commonly defined in <search.h> as:
struct qelem {
struct qelem *q_forw;
struct qelem *q_back;
};
Applications using these functions, however, were never able to
use this structure directly since it provided no room for the
actual data contained in the elements. Most applications defined
structures that contained the two pointers as the initial
elements and also provided space for, or pointers to, the
object's data. Applications that used these functions to update
more than one type of table also had the problem of specifying
two or more different structures with the same name, if they
literally used struct qelem as specified.
As described here, the implementations were actually expecting a
structure type where the first two members were forward and
backward pointers to structures. With C compilers that didn't
provide function prototypes, applications used structures as
specified in the DESCRIPTION above and the compiler did what the
application expected.
If this method had been carried forward with an ISO C standard
compiler and the historical function prototype, most applications
would have to be modified to cast pointers to the structures
actually used to be pointers to struct qelem to avoid compilation
warnings. By specifying void * as the argument type, applications
do not need to change (unless they specifically referenced struct
qelem and depended on it being defined in <search.h>).
Обоснование (Rationale)
None.
Будущие направления (Future directions)
None.
Смотри также (See also)
The Base Definitions volume of POSIX.1‐2017, search.h(0p)
