qsort(3p) [centos man page]
QSORT(3P) POSIX Programmer's Manual QSORT(3P) PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the correspond- ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux. NAME
qsort - sort a table of data SYNOPSIS
#include <stdlib.h> void qsort(void *base, size_t nel, size_t width, int (*compar)(const void *, const void *)); DESCRIPTION
The qsort() function shall sort an array of nel objects, the initial element of which is pointed to by base. The size of each object, in bytes, is specified by the width argument. If the nel argument has the value zero, the comparison function pointed to by compar shall not be called and no rearrangement shall take place. The application shall ensure that the comparison function pointed to by compar does not alter the contents of the array. The implementa- tion may reorder elements of the array between calls to the comparison function, but shall not alter the contents of any individual ele- ment. When the same objects (consisting of width bytes, irrespective of their current positions in the array) are passed more than once to the comparison function, the results shall be consistent with one another. That is, they shall define a total ordering on the array. The contents of the array shall be sorted in ascending order according to a comparison function. The compar argument is a pointer to the comparison function, which is called with two arguments that point to the elements being compared. The application shall ensure that the function returns an integer less than, equal to, or greater than 0, if the first argument is considered respectively less than, equal to, or greater than the second. If two members compare as equal, their order in the sorted array is unspecified. RETURN VALUE
The qsort() function shall not return a value. ERRORS
No errors are defined. The following sections are informative. EXAMPLES
None. APPLICATION USAGE
The comparison function need not compare every byte, so arbitrary data may be contained in the elements in addition to the values being compared. RATIONALE
The requirement that each argument (hereafter referred to as p) to the comparison function is a pointer to elements of the array implies that for every call, for each argument separately, all of the following expressions are nonzero: ((char *)p - (char *)base) % width == 0 (char *)p >= (char *)base (char *)p < (char *)base + nel * width FUTURE DIRECTIONS
None. SEE ALSO
The Base Definitions volume of IEEE Std 1003.1-2001, <stdlib.h> COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol- ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html . IEEE
/The Open Group 2003 QSORT(3P)
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LSEARCH(3P) POSIX Programmer's Manual LSEARCH(3P) PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the correspond- ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux. NAME
lsearch, lfind - linear search and update SYNOPSIS
#include <search.h> void *lsearch(const void *key, void *base, size_t *nelp, size_t width, int (*compar)(const void *, const void *)); void *lfind(const void *key, const void *base, size_t *nelp, size_t width, int (*compar)(const void *, const void *)); DESCRIPTION
The lsearch() function shall linearly search the table and return a pointer into the table for the matching entry. If the entry does not occur, it shall be added at the end of the table. The key argument points to the entry to be sought in the table. The base argument points to the first element in the table. The width argument is the size of an element in bytes. The nelp argument points to an integer containing the current number of elements in the table. The integer to which nelp points shall be incremented if the entry is added to the table. The compar argument points to a comparison function which the application shall supply (for example, strcmp()). It is called with two argu- ments that point to the elements being compared. The application shall ensure that the function returns 0 if the elements are equal, and non-zero otherwise. The lfind() function shall be equivalent to lsearch(), except that if the entry is not found, it is not added to the table. Instead, a null pointer is returned. RETURN VALUE
If the searched for entry is found, both lsearch() and lfind() shall return a pointer to it. Otherwise, lfind() shall return a null pointer and lsearch() shall return a pointer to the newly added element. Both functions shall return a null pointer in case of error. ERRORS
No errors are defined. The following sections are informative. EXAMPLES
Storing Strings in a Table This fragment reads in less than or equal to TABSIZE strings of length less than or equal to ELSIZE and stores them in a table, eliminating duplicates. #include <stdio.h> #include <string.h> #include <search.h> #define TABSIZE 50 #define ELSIZE 120 ... char line[ELSIZE], tab[TABSIZE][ELSIZE]; size_t nel = 0; ... while (fgets(line, ELSIZE, stdin) != NULL && nel < TABSIZE) (void) lsearch(line, tab, &nel, ELSIZE, (int (*)(const void *, const void *)) strcmp); ... Finding a Matching Entry The following example finds any line that reads "This is a test." . #include <search.h> #include <string.h> ... char line[ELSIZE], tab[TABSIZE][ELSIZE]; size_t nel = 0; char *findline; void *entry; findline = "This is a test. "; entry = lfind(findline, tab, &nel, ELSIZE, ( int (*)(const void *, const void *)) strcmp); APPLICATION USAGE
The comparison function need not compare every byte, so arbitrary data may be contained in the elements in addition to the values being compared. Undefined results can occur if there is not enough room in the table to add a new item. RATIONALE
None. FUTURE DIRECTIONS
None. SEE ALSO
hcreate(), tsearch(), the Base Definitions volume of IEEE Std 1003.1-2001, <search.h> COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol- ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html . IEEE
/The Open Group 2003 LSEARCH(3P)