qsort

Parameters

base

Pointer to the first object of the array to be sorted, converted to a void*.

num

Number of elements in the array pointed to by base.
size_t is an unsigned integral type.

size

Size in bytes of each element in the array.
size_t is an unsigned integral type.

compar

Pointer to a function that compares two elements.
This function is called repeatedly by qsort to compare two elements. It shall follow the following prototype:

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int compar (const void* p1, const void* p2);

Taking two pointers as arguments (both converted to const void*). The function defines the order of the elements by returning (in a stable and transitive manner):

return value	meaning
<0	The element pointed to by p1 goes before the element pointed to by p2
0	The element pointed to by p1 is equivalent to the element pointed to by p2
>0	The element pointed to by p1 goes after the element pointed to by p2

For types that can be compared using regular relational operators, a general compar function may look like:

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int compareMyType (const void * a, const void * b)
{
 if ( *(MyType*)a < *(MyType*)b ) return -1;
 if ( *(MyType*)a == *(MyType*)b ) return 0;
 if ( *(MyType*)a > *(MyType*)b ) return 1;
}

Return Value

Example

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/* qsort example */
#include <stdio.h> /* printf */
#include <stdlib.h> /* qsort */
int values[] = { 40, 10, 100, 90, 20, 25 };
int compare (const void * a, const void * b)
{
 return ( *(int*)a - *(int*)b );
}
int main ()
{
 int n;
 qsort (values, 6, sizeof(int), compare);
 for (n=0; n<6; n++)
 printf ("%d ",values[n]);
 return 0;
}

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Complexity

Data races

Exceptions (C++)

See also

bsearch

Binary search in array (function)