Thread: Problem with psprintf and intmax_t (%jd)

Dear all,

I'm facing a problem with psprintf and the %jd format string. I used
the following C-code:

PG_RETURN_CSTRING(psprintf("%d@%jd", (int)1, (intmax_t)2));

While this worked fine in past, I recently get (with PostgreSQL 13):

ERROR:  vsnprintf failed: Invalid argument with format string "%d@%jd"

I was not able to figure out what's the problem. Apparently this error
is thrown when vsnprintf(buf, len, fmt, args) in src/common/psprintf.c
returns a negative value. However, calling snprintf(buf, len, "%d@%jd",
(int)1, (intmax_t)2)) in a separate test program works fine on my
system.

I found a workaround. The following call works fine:

PG_RETURN_CSTRING(psprintf("%d@%lld", (int)1, (long long)2));

I could live with the workaround, but it is a bit scary, as I don't
really understand why "%jd" fails while "%lld" does not. Does anyone
know why, and/or is it possible for anyone else to reproduce the
problem?

Kind regards,
Jan Behrens

Jan Behrens <jbe-mlist@magnetkern.de> writes:
> I'm facing a problem with psprintf and the %jd format string. I used
> the following C-code:

> PG_RETURN_CSTRING(psprintf("%d@%jd", (int)1, (intmax_t)2));

> While this worked fine in past, I recently get (with PostgreSQL 13):

> ERROR:  vsnprintf failed: Invalid argument with format string "%d@%jd"

Before PG 12, this would have worked (on many platforms) if your
local libc's printf understood the "j" modifier.  Since v12, we use
src/port/snprintf.c on every platform, and it doesn't know "j".

By and large, we do not use the <stdint.h> types in Postgres, and are
unlikely to start doing so.  So this omission doesn't particularly
concern me.  "ll" with a cast to "long long" is indeed the recommended
practice if you want to print a 64-bit value.

            regards, tom lane