Re: [pgsql-hackers-win32] Repleacement for src/port/snprintf.c

Nicolai Tufar wrote:
> Hello all,
>
> I would like to submit my changes to src/port/snprintf.c to
> enable %n$ format placeholder replacement in snprintf() and
> vsnprintf(). Additionally I implemented a trivial printf().
>
> I also attach a diff for configure.in to include snprintf.o
> in pgport but I am sure it is not the right thing to do.
> Could someone give a hint on where I need to place such a
> definition.
>
> Please review my patch. as Tom Lane pointed out there
> are 150 messages in the following files that do not print
> properly:

It took me a while to understand this but I get it now. This is the
best explanation I have seen, from Linux 2.6:

One can also specify explicitly which argument is taken, at each place
where an argument is required, by writing '%m$' instead of '%' and '*m$'
instead of '*', where the decimal integer m denotes the position in the
argument list of the desired argument, indexed starting from 1. Thus,

printf("%*d", width, num);

and

printf("%2$*1$d", width, num);

are equivalent. The second style allows repeated references to the
same argument. The C99 standard does not include the style using '$',
which comes from the Single Unix Specification. If the style using '$'
is used, it must be used throughout for all conversions taking an
argument and all width and precision arguments, but it may be mixed with
'%%' formats which do not consume an argument. There may be no gaps in
the numbers of arguments specified using '$'; for example, if
arguments 1 and 3 are specified, argument 2 must also be specified
somewhere in the format string.

I can see why this would be useful for translations because it uncouples
the order of the printf arguments from the printf string. However, I
have learned that Win32, HP-UX, NetBSD 2.0, and BSD/OS do not support
this. This is probably because it is not in C99 but in SUS (see above).

Anyway, this is too large to put into 8.0, but I am attaching a patch
for 8.1 that has the proper configure tests to check if the C library
supports this behavior. If it does not, the build will use our
port/snprintf.c.

One problem with that is that our snprintf.c is not thread-safe. Seems
the increases use of it will require us to fix this soon. I have added
to TODO:

* Make src/port/snprintf.c thread-safe

One change to the original port is that there was a define of a union
with no name:

+ union{
+ void* value;
+ long_long numvalue;
+ double fvalue;
+ int charvalue;
+ };

As far as I know a union with no name is illegal. I just removed the
"union {" and the closing brace.

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