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qsort

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Revision as of 09:31, 27 November 2013 by Seishun (Talk | contribs)

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Defined in header <stdlib.h>
void qsort( void *ptr, size_t count, 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] Example

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

#include <stdio.h>
#include <stdlib.h>
 
int compare_ints(const void* a, const void* b)
{
    const int *arg1 = a;
    const int *arg2 = b;
 
    return *arg1 - *arg2;
}
 
int main(void)
{
    int i;
    int ints[] = { -2, 99, 0, -743, 2, 3, 4 };
    int size = sizeof ints / sizeof *ints;
 
    qsort(ints, size, sizeof(int), compare_ints);
 
    for (i = 0; i < size; i++) {
        printf("%d ", ints[i]);
    }
 
    printf("\n");
 
    return EXIT_SUCCESS;
}

Output:

-743 -2 0 2 3 4 99

[edit] See also

searches an array for an element of unspecified type
(function) [edit]