- size = vsnprintf(NULL, 0, fmt, ap2);
+ /*
+ * Some C libraries (Solaris, I'm looking at you) don't like
+ * an output buffer size of zero in vsnprintf, but will return
+ * sensible values given any non-zero buffer size. Hence, we
+ * use testbuf to gauge the length of the string.
+ */
+ size = vsnprintf(testbuf, 1, fmt, ap2);