Re: templated constanst

From:
"Javier Loureiro" <derethorspam@gmail.com>
Newsgroups:
comp.lang.c++.moderated
Date:
17 Jun 2006 06:13:08 -0400
Message-ID:
<1150453598.053379.18020@p79g2000cwp.googlegroups.com>
ups! the return type... I changed it, and recompile. I forgot the error
message, i?m sorry.

struct num_base
{
==>> MY_STCONS(bool, is_bounded, false);
         MY_STCONS(bool, is_exact, false);
};

D:\src\test\main.cpp(17) : error C2258: illegal pure syntax, must be '=
0'
D:\src\test\main.cpp(17) : error C2252: 'is_bounded' : pure specifier
can only be specified for functions

the fulll code is below again:

#define MY_STCONS(ty, name, val) static const ty name =
(ty)(val)

namespace mystd {

struct num_base
{
         MY_STCONS(bool, is_bounded, false);
         MY_STCONS(bool, is_exact, false);

};

template <class T>
struct num_procs : public num_base
{
    inline static T foo() { return T(0); }

};

struct num_int_base : public num_base
{
         MY_STCONS(bool, is_bounded, false);
         MY_STCONS(bool, is_exact, false);

};

template <> struct num_procs<int> : public num_int_base
{
    typedef int T;
    inline static T foo() { return T(20); }

};

int main (int argc, char **argv)
{
     return (0);
}

and the full log is :

--------------------Configuration: test - Win32
Debug--------------------
Compiling...
main.cpp
d:\src\test\main.cpp(7) : error C2258: illegal pure syntax, must be '=
0'
d:\src\test\main.cpp(7) : error C2252: 'is_bounded' : pure specifier
can only be specified for functions
d:\src\test\main.cpp(8) : error C2258: illegal pure syntax, must be '=
0'
d:\src\test\main.cpp(8) : error C2252: 'is_exact' : pure specifier can
only be specified for functions
d:\src\test\main.cpp(21) : error C2258: illegal pure syntax, must be '=
0'
d:\src\test\main.cpp(21) : error C2252: 'is_bounded' : pure specifier
can only be specified for functions
d:\src\test\main.cpp(22) : error C2258: illegal pure syntax, must be '=
0'
d:\src\test\main.cpp(22) : error C2252: 'is_exact' : pure specifier can
only be specified for functions
Error executing cl.exe.

test.exe - 8 error(s), 0 warning(s)

kanze ha escrito:

Javier Loureiro wrote:

I just read the "limits" header (included with visual 2003),
and it uses the macro :

 #define _STCONS(ty, name, val) static const ty name = (ty)(val)

to declare numeric_limits member variables like has_infinity,
is_integer, etc, inside a struct declaration...

I wrote this simple code using such macro and the limits class
inheritance, and it does not compile...

#define MY_STCONS(ty, name, val) static const ty name = (ty)(val)

namespace mystd {

struct num_base
{
        MY_STCONS(bool, is_bounded, false);
        MY_STCONS(bool, is_exact, false);
};

template <class T>
struct num_procs : public num_base
{
   inline static foo() { return T(0); }
};

struct num_int_base : public num_base
{
        MY_STCONS(bool, is_bounded, false);
        MY_STCONS(bool, is_exact, false);
};

template <> struct num_procs<int> : public num_int_base
{
   typedef int T;
   inline static foo() { return T(20); }
};


What's the error message? I see an obvious error in the fact
that you don't declare a return type for the functions foo(),
but that error should be clear from the error message. The rest
seems OK at first glance.


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