#include <search.h> void insque(void *element, void *pred); void remque(void *element);
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.
The following sections are informative.
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);
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);
The following example removes the element pointed to by element1.
#include <search.h> ... struct myque element1; ... remque (&element1);
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>).
Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .