Re: template size and speed
charles.lobo@gmail.com wrote:
I have recently begun using templates in C++ and have found it to be
quite useful. However, hearing stories of code bloat and assorted
problems I decided to write a couple of small programs to check. What I
expected was that there would be minor code bloat and some speed
improvement when using templates. However...
I wrote a basic list container (using templates), and a list container
(using virtual derived classes). I also tried with the std lib vector
class. I ran 1000000 inserts and accesses to all these lists and got
the following results (compiling on windows with microsoft compiler):
Size:
22,528 mytpl.exe
36,864 nonstd.exe
40,960 std.exe
The first is my template list, the second my non-template list, and the
third is using the std vector.
Without seeing your actual code, it's impossible to know what
you are really testing.
The first surprise was that my template list was actually *smaller*
than the non-template version! Very surprising.
Not really, if you only instantiated the template for a single
type. Calling a non-virtual function takes less space than
calling a virtual function, and the rest of the code should be
more or less identical.
Try using list<int>, list<long>, list<double>, etc. in a single
program. As you increase the number of different
instantiations, the template versions will probably grow faster
than the non-template versions. Probably, not certainly,
because there are well known techniques for factoring common
code out of the templates, and some compilers are also capable
of merging identical functions.
However, it's not all
good news. I then ran some timing tests.
Time:
875: running std.exe
1484: running nonstd.exe
1563: running mytpl.exe
As expected, the std vector is the fastest. However my template list
class is the *slowest*!!! This was definitly not expected.
Does anyone have any inputs on what's going on?
We'd have to see your code. And also, how you did your timing
tests. (And how you measured size as well; the size of the
executable file isn't necessarily very significant.)
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James Kanze (GABI Software) email:james.kanze@gmail.com
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