qsort descending order

[subramanian100in]

In the ISO document

www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf

in the detail of the qsort library function in 7.20.5.2, the
description says that, the contents of the array are sorted into
ascending order.

MY QUESTION:
Does it mean to include descending order also ?

If not, suppose we write the comparison function in such a way that it
returns less than, equal to, or greater than zero if the first
argument is greater than, equal to, or less than the second argument,
we should be able to use the qsort to sort the array elements into
descending order.

Am I correct or wrong ? Kindly explain.

 

[Richard Heathfield]

(e-mail address removed), India said:

In the ISO document

www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf

in the detail of the qsort library function in 7.20.5.2, the
description says that, the contents of the array are sorted into
ascending order.

MY QUESTION:
Does it mean to include descending order also ?

No. You define what "ascending" means in your comparison function, by
the way in which you associate the return value of the function with
the result of the comparison.

If not, suppose we write the comparison function in such a way that it
returns less than, equal to, or greater than zero if the first
argument is greater than, equal to, or less than the second argument,
we should be able to use the qsort to sort the array elements into
descending order.

Right.

 

[osmium]

In the ISO document

www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf

in the detail of the qsort library function in 7.20.5.2, the
description says that, the contents of the array are sorted into
ascending order.

MY QUESTION:
Does it mean to include descending order also ?

If not, suppose we write the comparison function in such a way that it
returns less than, equal to, or greater than zero if the first
argument is greater than, equal to, or less than the second argument,
we should be able to use the qsort to sort the array elements into
descending order.

Am I correct or wrong ? Kindly explain.

I think the word "ascending" should not have been used in the specification.

 

[Richard Bos]

I think the word "ascending" should not have been used in the specification.

Why not? qsort() sorts the array in ascending order, with respect to the
comparison function supplied. This can be ascending /qua/ numerical
size, ascending /qua/ age struct member, or ascending /qua/ _inverse_ of
the number of spots.

Richard

Richard

 

[CBFalconer]

In the ISO document

www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf

in the detail of the qsort library function in 7.20.5.2, the
description says that, the contents of the array are sorted into
ascending order.

MY QUESTION:
Does it mean to include descending order also ?

If not, suppose we write the comparison function in such a way that it
returns less than, equal to, or greater than zero if the first
argument is greater than, equal to, or less than the second argument,
we should be able to use the qsort to sort the array elements into
descending order.

Am I correct or wrong ? Kindly explain.

The only thing that defines order is the comparison function. So
you are correct.

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-- Francis Crick, co-discover of DNA
"There is nothing more amazing than stupidity in action."
-- Thomas Matthews

 

[Richard Tobin]

I think the word "ascending" should not have been used in the
specification.

[/QUOTE]

Why not?

Because, apparently, it is confusing. Of course you can say that
3,2,1 are in ascending order with respect to a comparison function
that says 1>2>3, but is it the clearest way to do it? The only problem
is finding a better terminology - perhaps the terms "earlier" and
"later" could have been used?

-- Richard