std::qsort

 

C++

Language

Standard library headers

Concepts

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

 

Algorithm library

Functions
Non-modifying sequence operations
all_of any_of none_of (C++11) (C++11) (C++11) for_each count count_if mismatch equal	find find_if find_if_not (C++11) find_end find_first_of adjacent_find search search_n
Modifying sequence operations
copy copy_if (C++11) copy_n (C++11) copy_backward move (C++11) move_backward (C++11) fill fill_n transform generate generate_n remove remove_if remove_copy remove_copy_if	replace replace_if replace_copy replace_copy_if swap swap_ranges iter_swap reverse reverse_copy rotate rotate_copy random_shuffle shuffle   (C++11) unique unique_copy
Partitioning operations
is_partitioned (C++11) partition partition_copy (C++11)	stable_partition partition_point (C++11)
Sorting operations (on sorted ranges)
is_sorted (C++11) is_sorted_until (C++11) sort	partial_sort partial_sort_copy stable_sort nth_element
Binary search operations (on sorted ranges)
lower_bound upper_bound	binary_search equal_range
Set operations (on sorted ranges)
merge inplace_merge includes	set_difference set_intersection set_symmetric_difference set_union
Heap operations
is_heap is_heap_until (C++11) make_heap	push_heap pop_heap sort_heap
Minimum/maximum operations
max max_element min min_element minmax (C++11) minmax_element (C++11)	lexicographical_compare is_permutation (C++11) next_permutation prev_permutation
Numeric operations
iota (C++11) accumulate inner_product	adjacent_difference partial_sum
C library
qsort	bsearch

 

Defined in header <cstdlib>
void qsort( const void *ptr, std::size_t count, std::size_t size,             int (*comp)(const void *, const void *) );

Sorts the given array pointed to by ptr in ascending order. The array contains count elements of size size. Function pointed to by comp is used for object comparison.

Parameters

ptr	-	pointer to the array to sort
count	-	number of element in the array
size	-	size of each element in the array in bytes
comp	-	comparison function which returns ​a negative integer value if the first argument is less than the second, a positive integer value if the first argument is greater than the second and zero if the arguments are equal. 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. ​

Return value

(none)

Notes

The type of the elements of the array must be a trivial type, otherwise the behavior is undefined.

Example

The following code sorts an array of integers using qsort().

#include <iostream>
#include <cstdlib>
 
int compare_ints(const void* a, const void* b)   // comparison function
{
    int arg1 = *reinterpret_cast<const int*>(a);
    int arg2 = *reinterpret_cast<const int*>(b);
    if(arg1 < arg2) return -1;
    if(arg1 > arg2) return 1;
    return 0;
}
 
int main()
{
    int a[] = { -2, 99, 0, -743, 2, 3, 4 };
    constexpr std::size_t size = sizeof(a)/sizeof(int);
 
    std::qsort(a, size, sizeof(int), compare_ints);
 
    for (int ai : a) std::cout << ai << ' ';
}

Output:

-743 -2 0 2 3 4 99

See also

bsearch	searches an array for an element of unspecified type (function)
sort	sorts a range into ascending order (function template)
is_trivial (C++11)	checks if a type is trivial (class template)
C documentation for qsort