Re: Variables in for loop (style issue)

Walter Bright <>
8 Jun 2006 06:27:29 -0400
James Dennett wrote:

Walter Bright wrote:

James Dennett wrote:

I've shown above that you cannot "just omit it".

#include <iostream>
#include <ostream>

void print(int r) { std::cout << r << '\n'; }

template <int i> class foo {};

int main()
     #define array_size 4
     int array[array_size];
     foo<array_size> object;

Compiles and works fine.

Yes, because you didn't just "omit the const", you used a
style that's largely obsolete in C++ because of its

While I see now that you could infer I meant do a global search replace
of const with nothing by "omit the const":
I actually was meaning not use the const in the first place.

And of course you missed the point of the
print() example, so I must have simplified that too much.
Consider a case where passing by const reference is a
significant optimization over pass by value; passing a
non-const reference just doesn't do the same job (can't
bind to temporaries, for one).

As I said in another post, your example is passing an integer literal,
for which passing by reference is not an optimization. There aren't
literals for UTDs which can benefit from pass by reference. Using a
literal which has special characteristics to justify an optimization
where a literal cannot be used anyway, regardless of const, doesn't
illustrate your point.

If you object to using a macro, I can suggest:
      enum { array_size = 4 };

Again, hardly a case of just omitting const.

It's even fewer characters (2 less) than const int array_size = 4;

Or I can argue that we're talking about const as a type qualifier, not
const as a storage class.

I'll defer to Daveed's opinion that const as specified by
the C++ standard is always a type qualifier; I don't find
your terminology helpful in this context.

As I pointed out in that thread, top level const does directly influence
the storage class as documented in the Standard. The Standard calls it a
type qualifier, but describes its behavior as a storage class. There's a
very clear documented major difference in behavior of const as top
level, and when it isn't top level.

My point was that you
CANNOT just drop the const and expect code to work, or even
to compile.

I do apologize for implying that one can do /const// on source code and
expect it to work, see above for what I meant.

There are workarounds ("hacks"?)

If you wish to dismiss 30 years of common C and C++ practice as a hack,
ok. The enum thing is common practice in C++. I can quote some of
Daveed's published code using it <g>.

You can find enum "hacks" and #defines for numerical constants in Boost
used regularly.

So I doubt I'm so far off base with it.

if you choose
to try to program in C++ without const, but significant
parts of the language are off-limits.

This isn't supported by the cases presented.

That aside, static type checking is just as strong
in C as in C++, so I don't see how static type checking is "more key to
C++". (*)

You know that there's a lot of code which your C compiler will
accept which will not type-check as C++ code, I'm pretty sure.

Some sample ways in which type checking is stronger and
more key to C++:

Disallowing implicit conversions from void* to other data
pointer types is one of the more obvious differences.

I know about the void* difference, and frankly find it trivial. I've
migrated quite a lot of code from C to C++, and converting:
        T *p = malloc(size);
        T *p = (T *)malloc(size);
here and there is not any big deal, and it never occurred to me that it
was regarded as a big advance in strong typechecking or key to anything,
because it isn't. It's a detail.

Types matter much more in C++ also as we can actually write code
which detects them and acts differently (e.g., via overloading,
or template type deduction). C++ also encourages more use of
UDTs, which as a style issue tends to lead to more mistakes
being caught by type checking (though good C programmers use
UDTs extensively also).

True, but none of that means that type checking is *stronger* in C++, it
just means that more use is made of it.

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