qsort, qsort_s
<stdlib.h>
int (*comp)(const void*, const void*, void*),
- count or size is greater than RSIZE_MAX
- ptr or comp is a null pointer (unless count is zero)
- As with all bounds-checked functions,
qsort_sis only guaranteed to be available if __STDC_LIB_EXT1__ is defined by the implementation and if the user defines __STDC_WANT_LIB_EXT1__ to the integer constant 1 before including <stdlib.h>.
If comp indicates two elements as equivalent, their order in the resulting sorted array is unspecified.
[edit] Parameters
The signature of the comparison function should be equivalent to the following:
int cmp(const void *a, const void *b);
The function must not modify the objects passed to it and must return consistent results when called for the same objects, regardless of their positions in the array.
[edit] Return value
[edit] Notes
Despite the name, neither C nor POSIX standards require this function to be implemented using quicksort or make any complexity or stability guarantees.
Unlike other bounds-checked functions, qsort_s does not treat arrays of zero size as a runtime constraint violation and instead returns successfully without altering the array (the other function that accepts arrays of zero size is bsearch_s).
The implementation of qsort_s in the Windows CRT is incompatible with the C standard. The Microsoft's version
is declared as:
void qsort_s(void *base, size_t num, size_t width,
int (*compare )(void *, const void *, const void *), void * context);.
It does not return a value, and the comparison function has a reversed parameter order with regard to the standard: the context is passed first.
[edit] Example
#include <limits.h> #include <stdio.h> #include <stdlib.h> int compare_ints(const void* a, const void* b) { int arg1 = *(const int*)a; int arg2 = *(const int*)b; if (arg1 < arg2) return -1; if (arg1 > arg2) return 1; return 0; // return (arg1 > arg2) - (arg1 < arg2); // possible shortcut // return arg1 - arg2; // erroneous shortcut: undefined behavior in case of // integer overflow, such as with INT_MIN here } int main(void) { int ints[] = {-2, 99, 0, -743, 2, INT_MIN, 4}; int size = sizeof ints / sizeof *ints; qsort(ints, size, sizeof(int), compare_ints); for (int i = 0; i < size; i++) printf ("%d ", ints[i]); printf ("\n"); }
Output:
-2147483648 -743 -2 0 2 4 99
[edit] References
- C23 standard (ISO/IEC 9899:2024):
- 7.22.5.2 The qsort function (p: TBD)
- K.3.6.3.2 The qsort_s function (p: TBD)
- C17 standard (ISO/IEC 9899:2018):
- 7.22.5.2 The qsort function (p: 258-259)
- K.3.6.3.2 The qsort_s function (p: 442-443)
- C11 standard (ISO/IEC 9899:2011):
- 7.22.5.2 The qsort function (p: 355-356)
- K.3.6.3.2 The qsort_s function (p: 609)
- C99 standard (ISO/IEC 9899:1999):
- 7.20.5.2 The qsort function (p: 319)
- C89/C90 standard (ISO/IEC 9899:1990):
- 4.10.5.2 The qsort function