Why this code must add sizeof()?

[nevergone]

Hello Everybody
In <<Modern C++ Design>Compile-Time Assertions
there is :
template <boolstruct CompileTimeChec ker
{
CompileTimeChec ker(...);
};

template <struct CompileTimeChec ker<false{ };

#define STATIC_CHECK(ex pr,msg) \
{ \
class ERROR_##msg {}; \
(void)sizeof( CompileTimeChec ker< (expr) !=
0>( (ERROR_##msg() ) )); \
}
//.....
so my question is why " (void)sizeof( CompileTimeChec ker< (expr) !=
0>( (ERROR_##msg() ) )); \" must add sizeof?
Thanks

[Default User]

aiooua wrote:

unlike what the book says, and what i expected i did not get any
error.
however, i got the following warning.

--
test.cpp:4: warning: ISO C++ forbids applying `sizeof' to a function
type
--

it seemed too simple to be a g++ bug, but i'll follow it on their
newsgroup.

The ISO C++ standard does not mandate "warnings" or "errors". Certain
conditions require a diagnostic. A warning is a diagnostic. It is quite
possible for a compiler to decide to continue with compilation,
especially if operating in a non-conforming mode so that it applies
various extensions.

Brian

[James Kanze]

On Apr 11, 6:58 am, "aiooua" <aio...@gmail.c omwrote:

On Apr 10, 8:34 pm, "James Kanze" <james.ka...@gm ail.comwrote:

On Apr 9, 2:34 pm, "aiooua" <aio...@gmail.c omwrote:

however, i have a related, but different problem. i tried the code as
printed in the book[#1] and couldn't get it to work.
---
/* begin code */
template<boolst ruct CompileTimeChec ker{ CompileTimeChec ker(...); };
template<struct CompileTimeChec ker<false{ };
#define STATIC_CHECK(ex pr, msg) { class ERROR_##msg {};
(void)sizeof(Co mpileTimeChecke r<(expr) != 0>((ERROR_##msg ()))); }

Are you sure you didn't forget a \ at the end of the previous
line? This line would make sense as part of the macro.

the macro was well-formed when i compiled, it got wrapped into two
lines (maybe because of line-length limits or something) while i
posted it here.

You mean that the line following the #define was actually on the
same line?

The reason I asked is because when I added the \ to the end of
the line with the #define, the code worked as expected (i.e.
failed to compile). (Of course, without the \, it failed to
compile as well.)

I'm not sure about the exact error message you got---it seems a

unlike what the book says, and what i expected i did not get any
error.
however, i got the following warning.

--
test.cpp:4: warning: ISO C++ forbids applying `sizeof' to a function
type
--

If I add the \ to the end of the line, I get:
cerr.cc: In function 'int main()':
cerr.cc:5: error: invalid application of 'sizeof' to a function
type
from g++. Both with no options, and with my usual options.
Maybe you have set some option somewhere to make g++ treat this
as a warning only.

--
James Kanze (GABI Software) email:ja******* **@gmail.com
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