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Date: Sun, 17 Jun 2012 21:26:44 +0200
From: Bruno Haible <bruno@...sp.org>
To: Rich Felker <dalias@...ifal.cx>, musl@...ts.openwall.com
Subject: setvbuf, __fbufsize bug
With musl-0.9.1: This program shows that after calling setvbuf to make
a stream buffered, it may in fact be unbuffered (__fbufsize returns 0).
This problems leads to a unit test failure in gnulib.
============================= foo.c =============================
#include <stdio.h>
#include <stdio_ext.h>
#include <stdlib.h>
#define TESTFILE "t-fbufmode.tmp"
int
main ()
{
FILE *fp;
char buf[5];
/* Create a file with some contents. */
fp = fopen (TESTFILE, "w");
if (fp == NULL)
goto skip;
if (fwrite ("foobarsh", 1, 8, fp) < 8)
goto skip;
if (fclose (fp))
goto skip;
/* Open it for reading. */
fp = fopen (TESTFILE, "r");
if (setvbuf (fp, NULL, _IONBF, 0))
goto skip;
if (__fbufsize (fp) > 0)
{
fprintf (stderr, "in unbuffered mode, __fbufsize returns > 0 !\n");
exit (1);
}
if (setvbuf (fp, buf, _IOFBF, 5) == 0)
{
if (__fbufsize (fp) == 0)
{
fprintf (stderr, "in buffered mode, __fbufsize returns 0 !\n");
exit (1);
}
}
fclose (fp);
return 0;
skip:
fprintf (stderr, "Skipping test: file operations failed.\n");
return 77;
}
======================================================================
$ musl-gcc foo.c -Wall
$ ./a.out
in buffered mode, __fbufsize returns 0 !
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