Re: I'd like to use STL algorithms
Dan McLeran ha scritto:
This approach calls for undefined behavior in the current C++ standard,
because binary_op is not allow to cause any side effects (in this case,
incrementing count is a side effect).
I didn't use a binary functor, I used a unary functor. I also don't
agree that incrementing an internal counter of a function object is a
side effect of calling transform with a unary functor.
Sorry, I incorrectly wrote binary_op but the same argument applies to a
unary op (see 25.2.3/2). About what constitutes a side-effect, my
statement is based on the definition given in 1.9/7 (emphasis added):
1.9/7: Accessing an object designated by a volatile lvalue (3.10),
*modifying an object*, calling a library I/O function, or calling a
function that does any of those operations are all side effects, which
are changes in the state of the execution environment.
Incrementing a counters is a modification of an object (the counter
itself) so it is a side effect according to this definition.
Anyway, even if we assume the relaxed wording of the draft (which
doesn't mention the term "side effect"), the code you posted is not
guaranteed to work as you expect.
Ganesh
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