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Sample of Defect

Project Name CID Checker Category Developer Description
ScummVM 1308097 USELESS_CALL Incorrect expression An extremely nice thing which was discovered only by Coverity. We have 2 class methods: clear() which clears the surface and empty() which checks whether the surface is 0 size. Native English speaker wanted to fill the screen with 0. He used incorrect call screen.empty(). Coverity gave a warning about a useless call, which let us catch this bug with much ease. Otherwise, we were seeing weird behaviour, while the code inspection was showing: here is screen emptying, proceed!
File: /engines/sherlock/tattoo/tattoo_journal.cpp 
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}

void TattooJournal::show() {
        Events &events = *_vm->_events;
        Resources &res = *_vm->_res;
        Screen &screen = *_vm->_screen;
        TattooUserInterface &ui = *(TattooUserInterface *)_vm->_ui;
        byte palette[PALETTE_SIZE];
        
        Common::Point oldScroll = screen._currentScroll;
        screen._currentScroll = Common::Point(0, 0);

        // Load journal images
        _journalImages = new ImageFile("journal.vgs");

        // Load palette
        Common::SeekableReadStream *stream = res.load("journal.pal");
        stream->read(palette, PALETTE_SIZE);
        ui.setupBGArea(palette);
        screen.translatePalette(palette);
        delete stream;

        // Set screen to black, and set background
        screen._backBuffer1.SHblitFrom((*_journalImages)[0], Common::Point(0, 0));
 
 <<< CID 1308097: Incorrect expression USELESS_CALL
 <<< Calling "screen->empty()" is only useful for its return value, which is ignored.
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        screen.empty();
        screen.setPalette(palette);

        if (_journal.empty()) {
                _up = _down = false;
        } else {
                drawJournal(0, 0);
        }
        drawControls(0);
        screen.slamRect(Common::Rect(0, 0, SHERLOCK_SCREEN_WIDTH, SHERLOCK_SCREEN_HEIGHT));

        _exitJournal = false;
        _scrollingTimer = 0;

        do {
                events.pollEventsAndWait();
                events.setButtonState();
                _wait = true;

                handleKeyboardEvents();
                highlightJournalControls(true);
                
                handleButtons();

                if (_wait)
                        events.wait(2);
Events:
side_effect_free tattoo_journal.cpp:69

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