-// ----------------------------------------------------------------------------
-// $Id$
-// ----------------------------------------------------------------------------
-// Public Domain C Library - http://pdclib.sourceforge.net
-// This code is Public Domain. Use, modify, and redistribute at will.
-// ----------------------------------------------------------------------------
-
-int ungetc( int c, FILE * stream ) { /* TODO */ };
+/* $Id$ */
+
+/* ungetc( int, 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>
+
+#ifndef REGTEST
+#include <_PDCLIB_io.h>
+
+int ungetc_unlocked( int c, FILE * stream )
+{
+ if ( c == EOF || stream->ungetidx == _PDCLIB_UNGETCBUFSIZE )
+ {
+ return -1;
+ }
+ return stream->ungetbuf[stream->ungetidx++] = (unsigned char) c;
+}
+
+int ungetc( int c, FILE * stream )
+{
+ flockfile( stream );
+ int r = ungetc_unlocked( c, stream );
+ funlockfile( stream);
+ return r;
+}
+
+#endif
+
+#ifdef TEST
+#include <_PDCLIB_test.h>
+#include <stdlib.h>
+
+const char* hellostr = "Hello, world!";
+
+int main( void )
+{
+ // Also see ftell() for some testing
+
+ // PDCLIB-18: fread ignores ungetc
+ size_t bufsz = strlen( hellostr ) + 1;
+ char * buf = malloc( bufsz );
+ FILE * fh;
+
+ // Also fgets
+ TESTCASE( ( fh = tmpfile() ) != NULL );
+ TESTCASE( fputs(hellostr, fh) == 0 );
+ rewind(fh);
+ TESTCASE( fgetc( fh ) == 'H' );
+ TESTCASE( ungetc( 'H', fh ) == 'H' );
+ TESTCASE( fgets( buf, bufsz, fh ) != NULL );
+ TESTCASE( strcmp( buf, hellostr ) == 0 );
+
+ // fread
+ rewind(fh);
+ TESTCASE( fgetc( fh ) == 'H' );
+ TESTCASE( ungetc( 'H', fh ) == 'H' );
+ TESTCASE( fread( buf, bufsz - 1, 1, fh ) == 1 );
+ TESTCASE( strncmp( buf, hellostr, bufsz - 1 ) == 0 );
+
+
+
+ return TEST_RESULTS;
+}
+
+#endif