On 06/12/2012 08:03 AM, Rich Felker wrote: > On Tue, Jun 12, 2012 at 06:12:39AM -0600, Eric Blake wrote: >> And this simple program proves that most libc know how to push back more >> than one byte, whether or not they differ from the original contents, >> and especially in the common case where the byte still fits in the >> buffer. It's the corner case where the bytes being pushed back differ >> from the backing store, and where they don't fit in the normal buffer >> (perhaps because you have used setvbuf or friends), and therefore libc >> has to malloc() some pushback storage, and if the malloc fails then so >> does the ungetc(). > > This is where we (musl vs glibc and perhaps you) have very different > design philosophies. Using a single non-switchable buffer simplifies > all the stdio code paths a lot, and reduces the cost of unget/get > cycles. I wouldn't look fondly on changing this for the sake of > supporting something that the standard says applications can't rely > upon.
We're talking past each other. I never said that ungetc() should support more than one pushback byte, only that most libc implementations already do support it as an extension. I fully agree with the current standards that say that at most one pushback byte is portable, and GNU m4 goes to great lengths to comply with that. Furthermore, I claim that musl need not go out its way to provide an extension where ungetc can be used for more than one byte. -- Eric Blake ebl...@redhat.com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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