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# std::qsort

From cppreference.com
< cpp‎ | algorithm

Defined in header `<cstdlib>` |  |
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.

### [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.

### [edit] Example

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

Run this code

    #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

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

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