Re: [9fans] what's wrong with this?

Re: [9fans] what's wrong with this?

[Russ Cox]

The problem is that assert tries to include the
text of what is being asserted, since the compiler
doesn't provide preprocessor variables for the
current file and line number.

Russ

Re: [9fans] what's wrong with this?

[Russ Cox]

the correct workaround is

#define assert(x) ((x) ? 0 : (_assert("x"), 0))

Re: [9fans] what's wrong with this?

[peter a. cejchan]

sape@plan9.bell-labs.com (Sape Mullender) wrote in message
[snip]
> For starters, it's abhorrently awful code.  You're also using macros recursively.
> Assert is a macro:
> 	#define	assert(x) if(x){}else _assert("x")
> Substitute it in your code and behold the mess you get.
>
> What are you trying to save with this macro anyway?
>
> 	Sape

eeeeeeeeeeeeeeeeeeeeeeeh! it isn't my code... just trying to ape-port
someone else's (jpeg-2000 standard codec (i depend on it with my
hi-quality compressed images)). could you, please, show me a correct
workaround (for the time being i just dropped assert()) ???

TIA, cheers,
++pac.

Re: [9fans] what's wrong with this?

[Ralph Corderoy]

Hi Charles,

> i was wondering whether the C assert macro was regarded as
> an expression or a statement, but as usual my C book isn't
> nearby.

Harbison and Steele say it acts as if it was

    void assert(int expr);

and if NDEBUG is #define'd then an implementation may #define assert to
be

    ((void)0)

Cheers,


Ralph.

Re: [9fans] what's wrong with this?

[Douglas A. Gwyn]

rog@vitanuova.com wrote:
> i always thought that:
> #define assert(x)       if(x){}else _assert("x")
> was a bit dodgy...

Yes, it should be:

extern void _assert(const char*);
#define	assert(x)	((x)?(void)0:_assert(#x))

Re: [9fans] what's wrong with this?

[Douglas A. Gwyn]

Charles Forsyth wrote:
> i was wondering whether the C assert macro was regarded as
> an expression or a statement, but as usual my C book isn't
> nearby.

The C standard requires that it expand to a void expression,
which of course should not have the -> operator applied to it.

Re: [9fans] what's wrong with this?

[rog]

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i always thought that:

#define	assert(x)	if(x){}else _assert("x")

was a bit dodgy... it's a good thing macros aren't
used much in plan 9 otherwise someone would
have been bitten.

still it's better than the ## nastiness, i suppose.

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From: "Russ Cox" <rsc@plan9.bell-labs.com>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] what's wrong with this?
Date: Fri, 27 Sep 2002 10:05:43 -0400
Message-ID: <b70f510fee137a3d8569f447c6f762e3@plan9.bell-labs.com>

The problem is that assert tries to include the
text of what is being asserted, since the compiler
doesn't provide preprocessor variables for the
current file and line number.

Russ

Re: [9fans] what's wrong with this?

[Charles Forsyth]

i was wondering whether the C assert macro was regarded as
an expression or a statement, but as usual my C book isn't
nearby.

[9fans] what's wrong with this?

[Peter A. Cejchan]

Dear friends,

8c complies "syntax error" when the following macro is called:

#define	jpc_bitstream_getbit_macro(bitstream) \
	(assert((bitstream)->openmode_ & JPC_BITSTREAM_READ), \
	  (--(bitstream)->cnt_ >= 0) ? \
	  (((bitstream)->buf_ >> (bitstream)->cnt_) & 1) : \
	  jpc_bitstream_fillbuf(bitstream))

int ret;
...
ret=jpc_bitstream_getbit_macro(bitstream);


TIA4help,
--
++pac.

Peter A. Cejchan
Paleobiology Lab, GLU Acad. Sci. CZ
<pac@next.gli.cas.cz>
[http | ftp]://next.gli.cas.cz

Re: [9fans] what's wrong with this?

[Sape Mullender]

> Dear friends,
>
> 8c complies "syntax error" when the following macro is called:
>
> #define	jpc_bitstream_getbit_macro(bitstream) \
> 	(assert((bitstream)->openmode_ & JPC_BITSTREAM_READ), \
> 	  (--(bitstream)->cnt_ >= 0) ? \
> 	  (((bitstream)->buf_ >> (bitstream)->cnt_) & 1) : \
> 	  jpc_bitstream_fillbuf(bitstream))
>
> int ret;
> ...
> ret=jpc_bitstream_getbit_macro(bitstream);

For starters, it's abhorrently awful code.  You're also using macros recursively.
Assert is a macro:
	#define	assert(x) if(x){}else _assert("x")
Substitute it in your code and behold the mess you get.

What are you trying to save with this macro anyway?

	Sape