[m-dev.] ODBC interface

[Fergus Henderson]

Simon TAYLOR, you wrote:
> +	/*
> +	** MR_setjmp(MR_jmp_buf *env)
> +	**
> +	** Save MR_engine_jmp_buf, then call setjmp(env).
> +	** setjmp can only occur as an expression, not a statement.
> +	** I'm not certain that this is 100% portable. K&R p254 states
> +	** that "a call to setjmp can only occur in certain contexts, 
> +	** basically the test of if, switch and loops, and only in
> +	** simple relational expressions". Is the expression below
> +	** a simple relational expression?
> +	*/
> +#define MR_setjmp(setjmp_env)						\
> +		(							\
> +			(setjmp_env)->mercury_env = MR_engine_jmp_buf,	\
> +			setjmp((setjmp_env)->env)			\
> +		)

No, it will not be simple relational expression.

	if (MR_setjmp(setjmp_env)) {

exands to

	if (( (setjmp_env)->mercury_env = MR_engine_jmp_buf,
		setjmp((setjmp_env)->env) )) {

which is not conforming ANSI C.
Instead it needs to be something like

	setjmp_env->mercury_env = MR_engine_jmp_buf;
	if (setjmp(setjmp_env->env)) {

Instead, I suggest you use either

	#define MR_pre_setjmp(setjmp_env) \
			((setjmp_env)->mercury_env = MR_engine_jmp_buf)
		
	#define MR_setjmp(setjmp_env) \
			setjmp((setjmp_env)->env)

with

	...
	MR_pre_setjmp(setjmp_env);
	if (MR_setjmp(setjmp_env)) {
		...
	}
	...

or

	#define MR_setjmp(setjmp_env, longjmp_label, fallthru_label)	\
		do {							\
			(setjmp_env)->mercury_env = MR_engine_jmp_buf;	\
			if (setjmp((setjmp_env)->env))			\
				goto longjmp_label;			\
			else						\
				goto fallthru_label;			\
		} while(0)

with

	...
	MR_setjmp(setjmp_env, longjmp_label, fallthru_label);
longjmp_label:
	...
fallthru_label:
	...

-- 
Fergus Henderson <fjh at cs.mu.oz.au>   |  "I have always known that the pursuit
WWW: <http://www.cs.mu.oz.au/~fjh>   |  of excellence is a lethal habit"
PGP: finger fjh at 128.250.37.3         |     -- the last words of T. S. Garp.