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std::qsort

From cppreference.com
< cpp‎ | algorithm
 
 
 
Defined in header <cstdlib>
extern "C" void qsort( void *ptr, std::size_t count, std::size_t size,
            int (*comp)(const void *, const void *) );
extern "C++" void qsort( 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 bytes. Function pointed to by comp is used for object comparison.

If comp indicates two elements as equivalent, their order is undefined.

Contents

[edit] 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.

[edit] Return value

(none)

[edit] Notes

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

The two overloads provided by the C++ standard library are distinct because the types of the parameter comp are distinct (language linkage is part of its type)

[edit] 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

[edit] See also

searches an array for an element of unspecified type
(function) [edit]
sorts a range into ascending order
(function template) [edit]
checks if a type is trivial
(class template) [edit]
C documentation for qsort