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Difference between revisions of "c/algorithm/qsort"

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< c‎ | algorithm
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void qsort( const void *ptr, size_t count, size_t size,
 
void qsort( const void *ptr, size_t count, size_t size,
 
             int (*comp)(const void *, const void *) );
 
             int (*comp)(const void *, const void *) );
 
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Sorts the given array pointed to by {{tt|ptr}} in ascending order. The array contains {{tt|count}} elements of {{tt|size}} bytes. Function pointed to by {{tt|comp}} is used for object comparison.
 
Sorts the given array pointed to by {{tt|ptr}} in ascending order. The array contains {{tt|count}} elements of {{tt|size}} bytes. Function pointed to by {{tt|comp}} is used for object comparison.
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===Parameters===
 
===Parameters===
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{{param list item | ptr | pointer to the array to sort}}
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{{par | ptr | pointer to the array to sort}}
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{{param list item | count | number of element in the array}}
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{{par | count | number of element in the array}}
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{{param list item | size | size of each element in the array in bytes}}
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{{par | size | size of each element in the array in bytes}}
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===Return value===
 
===Return value===
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===See also===
 
===See also===
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[[de:c/algorithm/qsort]]
 
[[de:c/algorithm/qsort]]

Revision as of 17:14, 31 May 2013

 
C
 
Algorithms
qsortqsort_s
(C11)
(C11)
 
Defined in header <stdlib.h>
void qsort( const 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

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 equivalent.

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.

​

Return value

(none)

Example

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

Run this code
#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

See also

Template:c/algorithm/dcl list bsearch
C++ documentation for qsort
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