On Mon, Jun 23, 2008 at 01:47:59PM +0200, Michael Kerrisk wrote:
> Right, here's another version. Could you please have another read
> through, Stephane
Michael,
it looks good to me.
I suspect it wasn't your intention to leave
> printf("n=%d, errno=%d\n", n, errno);
in though. That printf might set errno itself so that the next
check for errno wouldn't be valid.
>
> NOTES
> The GNU C library supports a non-standard extension that causes
> the library to dynamically allocate a string of sufficient size
> for input strings for the %s and %a[range] conversion
> specifiers. To make use of this feature, specify a as a length
> modifier (thus %as or %a[range]). The caller must free(3) the
> returned string, as in the following example:
>
> char *p;
> int n;
>
> errno = 0;
> n = scanf("%a[a-z]", &p);
> printf("n=%d, errno=%d\n", n, errno);
> if (n == 1) {
> printf("read: %s\n", p);
> free(p);
> } else if (errno != 0) {
> perror("scanf");
> } else {
> fprintf(stderr, "No matching characters\n"):
> }
>
> As shown in the above example, it is only necessary to call
> free(3) if the scanf() call successfully read a string.
>
> The a modifier is not available if the program is compiled with
> gcc -std=c99 or gcc -D_ISOC99_SOURCE (unless _GNU_SOURCE is
> also specified), in which case the a is interpreted as a speci-
> fier for floating point numbers (see above).
>
> Since version 2.7, glibc also provides the m modifier for the
> same purpose as the a modifier. The m modifier has the follow-
> ing advantages:
>
> * It may also be applied to %c conversion specifiers (e.g.,
> %3mc).
>
> * It avoids ambiguity with respect to the %a floating-point
> conversion specifier (and is unaffected by gcc -std=c99 etc.)
>
> * It is specified in the upcoming revision of the POSIX.1 stan-
> dard.
Cheers,
Stéphane
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