From f66022dda8d18e6732626c7806f6c4d32023d574 Mon Sep 17 00:00:00 2001 From: Rich Felker Date: Tue, 28 Aug 2018 19:16:40 -0400 Subject: [PATCH] make fmemopen's w+ mode truncate the buffer the w+ mode is specified to "truncate the buffer contents". like most of fmemopen, exactly what this means is underspecified. mode w and w+ of course implicitly 'truncate' the buffer if a write from the initial position is flushed, so in order for this part of the text about w+ not to be spurious, it should be interpreted as requiring something else, and the obvious reasonable interpretation is that the truncation is immediately visible if you attempt to read from the stream or the buffer before writing/flushing. this interpretation agrees with reported conformance test failures. --- src/stdio/fmemopen.c | 1 + 1 file changed, 1 insertion(+) diff --git a/src/stdio/fmemopen.c b/src/stdio/fmemopen.c index fb2656e3..5e0eeb50 100644 --- a/src/stdio/fmemopen.c +++ b/src/stdio/fmemopen.c @@ -112,6 +112,7 @@ FILE *fmemopen(void *restrict buf, size_t size, const char *restrict mode) if (!plus) f->f.flags = (*mode == 'r') ? F_NOWR : F_NORD; if (*mode == 'r') f->c.len = size; else if (*mode == 'a') f->c.len = f->c.pos = strnlen(buf, size); + else if (plus) *f->c.buf = 0; f->f.read = mread; f->f.write = mwrite; -- 2.25.1