What is the difference between the built-in qsort function and the stable sort function?

Question

From the various sources quoted, I know that the built-in C function, stable_sort is stable, but qsort is unstable. If so, then why do we use qsort at all? Isn't that redundant? Why not use stable_sort instead?

Answer 1

The reason for choosing fast sorting by stable sorting is mainly speed: qsortoften faster stable_sort, which should appear as not surprising, because it stable_sorthas a stronger guarantee.

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Answer 2

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merge sort.

Answer 3

, qsort?

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