At 01:18 PM 5/22/2002 -0400, Green, Paul wrote:
>Nicholas Clark [mailto:[EMAIL PROTECTED]] asks:
>> Note that sv.c has this in sv__gets:
>>
>> #if defined(VMS) && defined(PERLIO_IS_STDIO)
>> /* An ungetc()d char is handled separately from the regular
>> * buffer, so we getc() it back out and stuff it in the buffer.
>> */
>> i = PerlIO_getc(fp);
>> if (i == EOF) return 0;
>> *(--((*fp)->_ptr)) = (unsigned char) i;
>> (*fp)->_cnt++;
>> #endif
>>
>> How that code can know whether there is space at the start of
>> the buffer to do the stuffing, I don't know.
Good question. It does not compare _ptr with _base as the macro in iperlsys.h does.
>I wondered this too. I could only check our own implementation. We use the
>same trick of putting the ungetc's character right back into the input
>buffer. The reason it works is that (a) we only permit you to ungetc a
>single character,
How do you guarantee you'll never hit the code in PerlIOStdio_unread that
does ungetc inside a loop?
>and (b) we never fill the buffer unless we are reading a
>byte out of it too. So we NEVER have a case where the ungetc function can be
>called with the ptr on the first byte of the buffer.
I'm going to give the following a try and see what happens:
--- sv.c;-0 Sat May 18 18:59:19 2002
+++ sv.c Wed May 22 12:40:17 2002
@@ -5732,12 +5732,12 @@
#if defined(VMS) && defined(PERLIO_IS_STDIO)
/* An ungetc()d char is handled separately from the regular
- * buffer, so we getc() it back out and stuff it in the buffer.
+ * buffer, so we seek to our current position, which is a
+ * noop except for synching up ungetc()'s special 1-byte
+ * pushback buffer with the main stdio buffer.
*/
- i = PerlIO_getc(fp);
+ i = PerlSIO_fseek(fp, (Off_t) 0, SEEK_CUR);
if (i == EOF) return 0;
- *(--((*fp)->_ptr)) = (unsigned char) i;
- (*fp)->_cnt++;
#endif
/* Here is some breathtakingly efficient cheating */
[end of not yet a patch]
