Help with multi-sort

[Kurt _B]

What do you mean by this in the second sort? count-noidfiles

[David Crow]

FarPointer wrote:

Will this Suffice

No, because qsort() is not a stable sort. You would need to combine the effects of qsort_callbackName() and qsort_callbackAge() and call qsort() only once.

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"Let us be thankful for the fools. But for them the rest of us could not succeed." - Mark Twain

"There is no death, only a change of worlds." - Native American Proverb

[FarPointer]

Well what iam actually doing is that first i will sort with respect to the name ,then sort the sorteddata with respect to the age . int qsort_callback(const void * first, const void * second) { struct person *p1, * p2; p1 = (struct person *)first; p2 = (struct person *)second; //According to your preference if( (*(p1->Name)).Compare(*(p2->Name)) >0 ) { //for the age if(p1->Age > p2->Age) return 1; if(p1->Age < p2->Age) return -1; } //else same way as above } // Well here i have tried to make sorting in one go as David says qsort is not stable one but the previous one is more logical clear ,like if later we need a more customization on the sort you again sort on the sorted data Regards, FarPointer -- modified at 13:20 Friday 31st March, 2006

[FarPointer]

Wat do you mean by not a stable sort ,it should be a well tested and implemented one right(IMHO). Regards, FarPointer

[Kurt _B]

David Can you show me an example?

[David Crow]

Stable sorting algorithms maintain the relative order of records with equal keys. If whenever there are two records A and B with the same key and with A appearing before B in the original list, A will appear before B in the sorted list, the algorithm is said to be stable.

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"Let us be thankful for the fools. But for them the rest of us could not succeed." - Mark Twain

"There is no death, only a change of worlds." - Native American Proverb

[FarPointer]

Well thanks for making it clear . Regards, FarPointer

[David Crow]

int bynameinage( const void * v1, const void * v2 )
{
pmyData data1 = *(pmyData *) v1;
pmyData data2 = *(pmyData *) v2;

int dt = data1->age - data2->age;

if (dt != 0)
    return dt;

// same age so check name
return \_tcscmp(data1->name, data2->name);    

}
...
qsort(..., bynameinage);

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"Let us be thankful for the fools. But for them the rest of us could not succeed." - Mark Twain

"There is no death, only a change of worlds." - Native American Proverb

[David Crow]

FarPointer wrote:

...but the previous one is more logical clear ,like if later we need a more customization on the sort you again sort on the sorted data

For reasons already mentioned, calling qsort() again on the sorted list using a different key will not work.

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"Let us be thankful for the fools. But for them the rest of us could not succeed." - Mark Twain

"There is no death, only a change of worlds." - Native American Proverb

[FarPointer]

Neat and Clean. Regards, FarPointer

[Maximilien]

Thanks for the refresher course David. :)

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Maximilien Lincourt Your Head A Splode - Strong Bad