inconsistency of c/c++

[thomas]

Hi,
I have found one interesting thing.

the qsort() for c:
--------------c----
int compare (const void * a, const void * b)
{
return ( *(int*)a - *(int*)b ); -----(1)
}
qsort (values, 6, sizeof(int), compare);
-------------c++----
bool cmp(const int &a, const int &b){
return a<b; -----(2)
}
sort(values, values+6, cmp);
--------------------

We find that both sort the "values" array in ascending order, the first
(1) uses a converse comparison results with (2).
It says that if "compare" returns positive, we should put "a"
backwords for qsort; but if "cmp" returns true(like positive), we
should put "a" in front for sort.

 

[Victor Bazarov]

Hi,
I have found one interesting thing.

the qsort() for c:
--------------c----
int compare (const void * a, const void * b)
{
return ( *(int*)a - *(int*)b ); -----(1)
}
qsort (values, 6, sizeof(int), compare);
-------------c++----
bool cmp(const int &a, const int &b){
return a<b; -----(2)
}
sort(values, values+6, cmp);
--------------------

We find that both sort the "values" array in ascending order, the first
(1) uses a converse comparison results with (2).
It says that if "compare" returns positive, we should put "a"
backwords for qsort; but if "cmp" returns true(like positive), we
should put "a" in front for sort.

It's not an inconsistency, really. The 'qsort' uses a special
comparison functor, which is "greater", "equal", and "less" combined,
whereas 'std::sort' uses only 'less'.

Change the word "positive" in your statement which starts with "It
says.." to "negative", and there is no "but". If "compare" returns
negative qsort will put 'a' before 'b', so will 'sort' if "cmp" returns
"true".

V