Re: FreeTDS port to VMS V9.x on x86?

On 6/23/2025 6:33 PM, Craig A. Berry wrote:

I haven't had time yet to dig into why the replacement wasn't working.

I did a little digging.
tds_vasprintf contains:
// fp = NLA0:
len = vfprintf(fp, fmt, ap);
// buf = malloc(len + 1)
if (vsprintf(buf, fmt, ap) != len)
     return -1;
And the test fails.
And it can be recreated outside of FreeTDS.
$ type zzzz.c
#include <stdio.h>
#include <stdarg.h>
void test(const char *fmt, ...)
{
     va_list ap;
     va_start(ap, fmt);
     int len_1 = vfprintf(stdout, fmt, ap);
//    va_end(ap);
     fprintf(stdout, " [len=%d]\n", len_1);
     char buf[1000];
//    va_start(ap, fmt);
     int len_2 = vsprintf(buf, fmt, ap);
     va_end(ap);
     printf("%s [len=%d]\n", buf,len_2);
}
int main(int argc, char *argv[])
{
     test("INSERT INTO t1 VALUES(%d, '%s')", 999, "XXX");
     test("INSERT INTO t1 VALUES(%d, '%s')", 999, "XXX");
     test("INSERT INTO t1 VALUES(%d, '%s')", 999, "XXX");
     return 0;
}
$ cc zzzz
$ link zzzz
$ r zzzz
INSERT INTO t1 VALUES(999, 'XXX') [len=33]
INSERT INTO t1 VALUES(2060040508, '') [len=37]
INSERT INTO t1 VALUES(999, 'XXX') [len=33]
INSERT INTO t1 VALUES(2068038401, '') [len=37]
INSERT INTO t1 VALUES(999, 'XXX') [len=33]
INSERT INTO t1 VALUES(2068038401, '') [len=37]
It seems like vfprintf mess up ap so it is no longer good
for vsprintf.
And that is supposedly perfectly legal. C99 says:
<quote>
As the functions vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf, and
vsscanf invoke the va_arg macro, the value of arg after the return is indeterminate.
</quote>
Unfortunately that means that the entire fallback algorithm
in tds_vasprintf (write to null device to find output size,
allocate buffer of correct size and then write to buffer)
is broken.
Arne