qsort.3p (3998B)
- '\" et
- .TH QSORT "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
- .\"
- .SH 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.
- .\"
- .SH NAME
- qsort
- \(em sort a table of data
- .SH SYNOPSIS
- .LP
- .nf
- #include <stdlib.h>
- .P
- void qsort(void *\fIbase\fP, size_t \fInel\fP, size_t \fIwidth\fP,
- int (*\fIcompar\fP)(const void *, const void *));
- .fi
- .SH DESCRIPTION
- The functionality described on this reference page is aligned with the
- ISO\ C standard. Any conflict between the requirements described here and the
- ISO\ C standard is unintentional. This volume of POSIX.1\(hy2017 defers to the ISO\ C standard.
- .P
- The
- \fIqsort\fR()
- function shall sort an array of
- .IR nel
- objects, the initial element of which is pointed to by
- .IR base .
- The size of each object, in bytes, is specified by the
- .IR width
- argument. If the
- .IR nel
- argument has the value zero, the comparison function pointed to by
- .IR compar
- shall not be called and no rearrangement shall take place.
- .P
- The application shall ensure that the comparison function pointed to by
- .IR compar
- does not alter the contents of the array. The implementation may
- reorder elements of the array between calls to the comparison function,
- but shall not alter the contents of any individual element.
- .P
- 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.
- .P
- The contents of the array shall be sorted in ascending order according
- to a comparison function. The
- .IR 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.
- .SH "RETURN VALUE"
- The
- \fIqsort\fR()
- function shall not return a value.
- .SH ERRORS
- No errors are defined.
- .LP
- .IR "The following sections are informative."
- .SH EXAMPLES
- None.
- .SH "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.
- .SH RATIONALE
- The requirement that each argument (hereafter referred to as
- .IR 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 non-zero:
- .sp
- .RS 4
- .nf
- ((char *)p - (char *)base) % width == 0
- (char *)p >= (char *)base
- (char *)p < (char *)base + nel * width
- .fi
- .P
- .RE
- .SH "FUTURE DIRECTIONS"
- None.
- .SH "SEE ALSO"
- .IR "\fIalphasort\fR\^(\|)"
- .P
- The Base Definitions volume of POSIX.1\(hy2017,
- .IR "\fB<stdlib.h>\fP"
- .\"
- .SH COPYRIGHT
- Portions of this text are reprinted and reproduced in electronic form
- from IEEE Std 1003.1-2017, Standard for Information Technology
- -- Portable Operating System Interface (POSIX), The Open Group Base
- Specifications Issue 7, 2018 Edition,
- Copyright (C) 2018 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 .
- .PP
- 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 .