make vfprintf set stream orientation even for zero-length output

if no output is produced, no underlying fwrite will ever be called,
but byte-oriented printf functions are still required to set the
orientation of the stream to byte-oriented. call __towrite explicitly
if the FILE is not already in write mode.

diff --git a/src/stdio/vfprintf.c b/src/stdio/vfprintf.c
index af069d133c8dacd5d7172bd3512d4c5925760344..2100eb5e5449eb73bcea71792edb0096ba68795a 100644 (file)
--- a/src/stdio/vfprintf.c
+++ b/src/stdio/vfprintf.c
@@ -678,7 +678,8 @@ int vfprintf(FILE *restrict f, const char *restrict fmt, va_list ap)
                f->buf_size = sizeof internal_buf;
                f->wpos = f->wbase = f->wend = 0;
        }
-       ret = printf_core(f, fmt, &ap2, nl_arg, nl_type);
+       if (!f->wend && __towrite(f)) ret = -1;
+       else ret = printf_core(f, fmt, &ap2, nl_arg, nl_type);
        if (saved_buf) {
                f->write(f, 0, 0);
                if (!f->wpos) ret = -1;