Re: static const int optimization fails in conditional expressions

[Phil Edwards <pedwards@disaster.jaj.com>]

On Tue, Dec 11, 2001 at 05:06:31PM -0600, James Jurach wrote:
> When class members declared as static const int appear in conditional
> expressions, they are not properly optimized out.  The compiler treats them
> as undefined variables, rather than integer literals.

That's because they /are/ undefined variables, not integer literals.
Integer literals are 17, 42, and -3, not Foo::erf, regardless of how
unchanging Foo::erf may be.

Static class member variables must always be /defined/.  That means they
must be given a variable definition in one-and-only-one translation unit,
outside the class declaration.  Some compilers will let you get away with
this sloppiness; gcc 3+ will not.


    % cat fixed_condexpr.cc
    #include <iostream>

    struct Foo
    {
      static const int erf = 0;
      static const int foo = 1;
    };

->  const int Foo::erf;
->  const int Foo::foo;

    int main(int argc, char**)
    {
      std::cout << "foo: " << (argc%2 ? Foo::erf : Foo::foo) << std::endl;
      return 0;
    }

    % g++-3.0 -Wall -W fixed_condexpr.cc
    % ./a.out
    foo: 0
    % ./a.out x
    foo: 1
    %

Phil

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