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32 .\" @(#)qsort.3 8.1 (Berkeley) 6/4/93
56 .Fa "int \*[lp]*compar\*[rp]\*[lp]const void *, const void *\*[rp]"
63 .Fa "int \*[lp]^compar\*[rp]\*[lp]const void *, const void *\*[rp]"
71 .Fa "int \*[lp]*compar\*[rp]\*[lp]void *, const void *, const void *\*[rp]"
78 .Fa "int \*[lp]*compar\*[rp]\*[lp]const void *, const void *\*[rp]"
85 .Fa "int \*[lp]^compar\*[rp]\*[lp]const void *, const void *\*[rp]"
92 .Fa "int \*[lp]*compar\*[rp]\*[lp]const void *, const void *\*[rp]"
99 .Fa "int \*[lp]^compar\*[rp]\*[lp]const void *, const void *\*[rp]"
104 function is a modified partition-exchange sort, or quicksort.
107 function is a modified selection sort.
110 function is a modified merge sort with exponential search
111 intended for sorting data with pre-existing order.
117 functions sort an array of
119 objects, the initial member of which is pointed to by
121 The size of each object is specified by
126 behaves similarly, but
131 .Dq "sizeof(void *) / 2" .
133 The contents of the array
135 are sorted in ascending order according to
136 a comparison function pointed to by
138 which requires two arguments pointing to the objects being
141 The comparison function must return an integer less than, equal to, or
142 greater than zero if the first argument is considered to be respectively
143 less than, equal to, or greater than the second.
147 function behaves identically to
149 except that it takes an additional argument,
151 which is passed unchanged as the first argument to function pointed to
153 This allows the comparison function to access additional
154 data without using global variables, and thus
156 is suitable for use in functions which must be reentrant.
159 function behaves identically to
161 except that it takes a block, rather than a function pointer.
163 The algorithms implemented by
170 stable, that is, if two members compare as equal, their order in
171 the sorted array is undefined.
174 function behaves identically to
176 except that it takes a block, rather than a function pointer.
182 function behaves identically to
184 except that it takes a block, rather than a function pointer.
190 functions are an implementation of C.A.R.
194 a variant of partition-exchange sorting; in particular, see
198 takes O N lg N average time.
199 This implementation uses median selection to avoid its
200 O N**2 worst-case behavior.
204 function is an implementation of
205 .An "J.W.J. William" Ns 's
208 a variant of selection sorting; in particular, see
209 .An "D.E. Knuth" Ns 's
212 takes O N lg N worst-case time.
217 is that it uses almost no additional memory; while
219 does not allocate memory, it is implemented using recursion.
223 requires additional memory of size
226 bytes; it should be used only when space is not at a premium.
230 is optimized for data with pre-existing order; its worst case
231 time is O N lg N; its best case is O N.
239 Memory availability and pre-existing order in the data can make this
249 .Rv -std heapsort mergesort
251 A sample program that sorts an array of
253 values in place using
255 and then prints the sorted array to standard output is:
261 * Custom comparison function that compares 'int' values through pointers
262 * passed by qsort(3).
265 int_compare(const void *p1, const void *p2)
267 int left = *(const int *)p1;
268 int right = *(const int *)p2;
270 return ((left > right) - (left < right));
274 * Sort an array of 'int' values and print it to standard output.
279 int int_array[] = { 4, 5, 9, 3, 0, 1, 7, 2, 8, 6 };
280 size_t array_size = sizeof(int_array) / sizeof(int_array[0]);
283 qsort(&int_array, array_size, sizeof(int_array[0]), int_compare);
284 for (k = 0; k < array_size; k++)
285 printf(" %d", int_array[k]);
287 return (EXIT_SUCCESS);
293 did not permit the comparison routine itself to call
295 This is no longer true.
301 functions succeed unless:
306 argument is zero, or,
312 .Dq "sizeof(void *) / 2" .
319 were unable to allocate memory.
328 .%J "The Computer Journal"
336 .%J "Communications of the ACM"
343 .%B "The Art of Computer Programming"
345 .%T "Sorting and Searching"
346 .%P pp. 114-123, 145-149
350 .%T "Optimistic Sorting and Information Theoretic Complexity"
351 .%J "Fourth Annual ACM-SIAM Symposium on Discrete Algorithms"
357 .%T "Engineering a Sort Function"
358 .%J "Software--Practice and Experience"
370 The variants of these functions that take blocks as arguments first appeared in
372 This implementation was created by David Chisnall.