Re: std::set, index of element
On 2009-01-16 12:33:50 -0500, "Hicham Mouline" <firstname.lastname@example.org> said:
"Pete Becker" <email@example.com> wrote in message
On 2009-01-16 08:38:26 -0500, "Hicham Mouline" <firstname.lastname@example.org> said:
CalcOperationSet is a std::set, and so finding the index of the operation
inside the set,
using std::distance is not ideal.
I just switched to std::map< CalcOperation, size_t >, wrapper by
and I actually store the index of each operation.
It is twice as fast than std::set in this usage case.
Let's be clear about what this means: you changed the kind of container
and changed how you track locations, and the result is faster. map and set
typically use the same code under the covers. The difference you see comes
from changing how you track locations.
With a set, i used to find the index of the operation with std::distance()
which is slow.
With the map<Operation, size_t>, I actually stored the index as the value,
so all that
was involved is the  operator to read the index directly.
It makes sense it is faster.
Yes, I understood that. The difference in speed comes from storing the
index, not from changing the data structure. You could put the index
into the set and get the same results.
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Standard C++ Library Extensions: a Tutorial and Reference
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