Test whether change_filename_extension succeeded before using its output

common/include/strutil.h

@@ -61,7 +61,8 @@ struct splitpath_t
 void removeext(const char *filename, std::array<char, 20> &out);
 
 //give a filename a new extension, doesn't work with paths with no extension already there
-void change_filename_extension(std::span<char> dest, const char *src, std::span<const char, 4> ext);
+[[nodiscard]]
+bool change_filename_extension(std::span<char> dest, const char *src, std::span<const char, 4> ext);
 
 /* Given an MS-DOS path, return pointers to the start of the basename and the
  * start of the extension.

common/misc/strutil.cpp

@@ -136,16 +136,17 @@ void removeext(const char *const filename, std::array<char, 20> &out)
 }
 
 //give a filename a new extension, won't append if strlen(dest) > 8 chars.
-void change_filename_extension(const std::span<char> dest, const char *const src, const std::span<const char, 4> ext)
+bool change_filename_extension(const std::span<char> dest, const char *const src, const std::span<const char, 4> ext)
 {
 	const char *const p = strrchr(src, '.');
 	const std::size_t src_dist_to_last_dot = p ? std::distance(src, p) : strlen(src);
 	if (src_dist_to_last_dot + 1 + ext.size() > dest.size())
 	{
 		dest.front() = 0;
-		return;	// a non-opened file is better than a bad memory access
+		return false;	// a non-opened file is better than a bad memory access
 	}
 	std::snprintf(dest.data(), dest.size(), "%.*s.%s", static_cast<int>(src_dist_to_last_dot), src, ext.data());
+	return true;
 }
 
 splitpath_t d_splitpath(const char *name)

d2x-rebirth/main/movie.cpp

@@ -518,7 +518,11 @@ static int init_subtitles(d_loaded_subtitle_state &SubtitleState, const std::spa
 
 	if (!ifile) {								//no text version, try binary version
 		std::array<char, FILENAME_LEN> filename2;
-		change_filename_extension(filename2, filename.data(), "txb");
+		if (!change_filename_extension(filename2, filename.data(), "txb"))
+		{
+			con_printf(CON_NORMAL, "Rebirth: skipping subtitles because cannot open \"%s\" (\"%s\")", filename.data(), PHYSFS_getErrorByCode(physfserr));
+			return 0;
+		}
 		auto &&[ifile2, physfserr2] = PHYSFSX_openReadBuffered(filename2.data());
 		if (!ifile2)
 		{

similar/main/bm.cpp

@@ -538,7 +538,11 @@ void load_robot_replacements(const d_fname &level_name)
 	auto &Robot_joints = LevelSharedRobotJointState.Robot_joints;
 	int t,j;
 	std::array<char, FILENAME_LEN> ifile_name;
-	change_filename_extension(ifile_name, level_name, "HXM");
+	if (!change_filename_extension(ifile_name, level_name, "HXM"))
+	{
+		con_printf(CON_URGENT, "Failed to generate HXM name from level name \"%s\"", level_name.data());
+		return;
+	}
 
 	auto fp = PHYSFSX_openReadBuffered(ifile_name.data()).first;
 	if (!fp)		//no robot replacement file

similar/main/gamesave.cpp

@@ -1845,12 +1845,18 @@ static int save_level_sub(
 	}
 //	else
 	{
+		auto &level_file_extension =
 #if defined(DXX_BUILD_DESCENT_II)
-		if (Gamesave_current_version > 3)
-			change_filename_extension(temp_filename, filename, D2X_LEVEL_FILE_EXTENSION);
-		else
+			(Gamesave_current_version > 3)
+			? D2X_LEVEL_FILE_EXTENSION
+			:
 #endif
-			change_filename_extension(temp_filename, filename, D1X_LEVEL_FILE_EXTENSION);
+			D1X_LEVEL_FILE_EXTENSION;
+		if (!change_filename_extension(temp_filename, filename, level_file_extension))
+		{
+			con_printf(CON_URGENT, "Failed to generate filename for level data from \"%s\"", filename);
+			return 1;
+		}
 	}
 
 	auto &&[SaveFile, physfserr] = PHYSFSX_openWriteBuffered(temp_filename.data());

similar/main/menu.cpp

@@ -876,7 +876,8 @@ static window_event_result demo_menu_keycommand( listbox *lb,const d_event &even
 
 				// Get backup name
 				const auto ic = items[citem];
-				change_filename_extension(bakname, ic, DEMO_BACKUP_EXT);
+				if (!change_filename_extension(bakname, ic, DEMO_BACKUP_EXT))
+					return window_event_result::handled;
 				const auto x = nm_messagebox(menu_title{nullptr}, 2, TXT_YES, TXT_NO,	"Are you sure you want to\n"
 								  "swap the endianness of\n"
 								  "%s? If the file is\n"

similar/main/newdemo.cpp

@@ -4360,11 +4360,9 @@ int newdemo_swap_endian(const char *filename)
 	infile.reset();
 	outfile.reset();
 
-	if (complete)
+	std::array<char, PATH_MAX> bakpath;
+	if (complete && change_filename_extension(bakpath, inpath, DEMO_BACKUP_EXT))
 	{
-		std::array<char, PATH_MAX> bakpath;
-
-		change_filename_extension(bakpath, inpath, DEMO_BACKUP_EXT);
 		PHYSFSX_rename(inpath, bakpath.data());
 		PHYSFSX_rename(DEMO_FILENAME, inpath);
 	}

similar/main/piggy.cpp

@@ -1542,9 +1542,11 @@ static void piggy_write_pigfile(const std::span<const char, FILENAME_LEN> filena
 	data_offset = bitmap_data_start;
 
 	std::array<char, FILENAME_LEN> tname;
-	change_filename_extension(tname, filename.data(), "lst");
+	if (!change_filename_extension(tname, filename.data(), "lst"))
+		return;
 	auto fp1 = PHYSFSX_openWriteBuffered(tname.data()).first;
-	change_filename_extension(tname, filename.data(), "all");
+	if (!change_filename_extension(tname, filename.data(), "all"))
+		return;
 	auto fp2 = PHYSFSX_openWriteBuffered(tname.data()).first;
 
 	for (i=1; i < Num_bitmap_files; i++ ) {
@@ -1785,7 +1787,8 @@ void load_bitmap_replacements(const std::span<const char, FILENAME_LEN> level_na
 	free_bitmap_replacements();
 
 	std::array<char, FILENAME_LEN> ifile_name;
-	change_filename_extension(ifile_name, level_name.data(), "POG");
+	if (!change_filename_extension(ifile_name, level_name.data(), "POG"))
+		return;
 	if (auto ifile = PHYSFSX_openReadBuffered(ifile_name.data()).first)
 	{
 		int id,version;