Fixed safeguard calculation in ftell().

[pdclib] / functions / stdio / ftell.c

diff --git a/functions/stdio/ftell.c b/functions/stdio/ftell.c
index d531292d0147c647be160a4a425f0bb370064400..29c360a2fd55d82f1d8569c67c6c3332e5f7fef2 100644 (file)
--- a/functions/stdio/ftell.c
+++ b/functions/stdio/ftell.c
@@ -1,8 +1,95 @@
-// ----------------------------------------------------------------------------
-// $Id$
-// ----------------------------------------------------------------------------
-// Public Domain C Library - http://pdclib.sourceforge.net
-// This code is Public Domain. Use, modify, and redistribute at will.
-// ----------------------------------------------------------------------------
-
-long ftell( FILE * stream ) { /* TODO */ };
+/* $Id$ */
+
+/* ftell( FILE * )
+
+   This file is part of the Public Domain C Library (PDCLib).
+   Permission is granted to use, modify, and / or redistribute at will.
+*/
+
+#include <stdio.h>
+#include <limits.h>
+
+#ifndef REGTEST
+
+long int ftell( struct _PDCLIB_file_t * stream )
+{
+    /* ftell() must take into account:
+       - the actual *physical* offset of the file, i.e. the offset as recognized
+         by the operating system (and stored in stream->pos.offset); and
+       - any buffers held by PDCLib, which
+         - in case of unwritten buffers, count in *addition* to the offset; or
+         - in case of unprocessed pre-read buffers, count in *substraction* to
+           the offset. (Remember to count ungetidx into this number.)
+       Conveniently, the calculation ( ( bufend - bufidx ) + ungetidx ) results
+       in just the right number in both cases:
+         - in case of unwritten buffers, ( ( 0 - unwritten ) + 0 )
+           i.e. unwritten bytes as negative number
+         - in case of unprocessed pre-read, ( ( preread - processed ) + unget )
+           i.e. unprocessed bytes as positive number.
+       That is how the somewhat obscure return-value calculation works.
+    */
+    /*  If offset is too large for return type, report error instead of wrong
+        offset value.
+    */
+    /* TODO: Check what happens when ungetc() is called on a stream at offset 0 */
+    if ( ( stream->pos.offset - stream->bufend ) > ( LONG_MAX - ( stream->bufidx - stream->ungetidx ) ) )
+    {
+        /* integer overflow */
+        _PDCLIB_errno = _PDCLIB_ERANGE;
+        return -1;
+    }
+    return (long int)( stream->pos.offset - ( ( (int)stream->bufend - (int)stream->bufidx ) + stream->ungetidx ) );
+}
+
+#endif
+
+#ifdef TEST
+#include <_PDCLIB_test.h>
+
+#include <stdlib.h>
+
+int main( void )
+{
+    /* Testing all the basic I/O functions individually would result in lots
+       of duplicated code, so I took the liberty of lumping it all together
+       here.
+    */
+    /* The following functions delegate their tests to here:
+       fgetc fflush rewind fputc ungetc fseek
+       flushbuffer seek fillbuffer prepread prepwrite
+    */
+    char * buffer = (char*)malloc( 4 );
+    FILE * fh;
+    TESTCASE( ( fh = tmpfile() ) != NULL );
+    TESTCASE( setvbuf( fh, buffer, _IOLBF, 4 ) == 0 );
+    TESTCASE( fputc( '1', fh ) == '1' );
+    TESTCASE( fputc( '2', fh ) == '2' );
+    TESTCASE( fputc( '3', fh ) == '3' );
+    /* Positions incrementing as expected? */
+    TESTCASE( ftell( fh ) == 3l );
+    TESTCASE_NOREG( fh->pos.offset == 0l );
+    TESTCASE_NOREG( fh->bufidx == 3l );
+    /* Buffer properly flushed when full? */
+    TESTCASE( fputc( '4', fh ) == '4' );
+    TESTCASE_NOREG( fh->pos.offset == 4l );
+    TESTCASE_NOREG( fh->bufidx == 0 );
+    /* fflush() resetting positions as expected? */
+    TESTCASE( fputc( '5', fh ) == '5' );
+    TESTCASE( fflush( fh ) == 0 );
+    TESTCASE( ftell( fh ) == 5l );
+    TESTCASE_NOREG( fh->pos.offset == 5l );
+    TESTCASE_NOREG( fh->bufidx == 0l );
+    /* rewind() resetting positions as expected? */
+    rewind( fh );
+    TESTCASE( ftell( fh ) == 0l );
+    TESTCASE_NOREG( fh->pos.offset == 0 );
+    TESTCASE_NOREG( fh->bufidx == 0 );
+    /* Reading back first character after rewind for basic read check */
+    TESTCASE( fgetc( fh ) == '1' );
+    /* TODO: t.b.c. */
+    TESTCASE( fclose( fh ) == 0 );
+    return TEST_RESULTS;
+}
+
+#endif
+