c++ - 提取图标Ex : works but occasionally crashes

Question

我正在从文件中提取图标并在对话框中显示它们

const LPCWSTR path = L"c:\path\to\file";
const UINT nIconsCheck = ExtractIconEx(path, -1, nullptr, nullptr, 0);
if(nIconsCheck > 0)
{
    HICON *iconHandles=new HICON;
    const UINT nIcons = ExtractIconEx(path, 0, iconHandles, nullptr, nIconsCheck);

    if(nIcons == nIconsCheck && nIcons != unsigned(-1))
    {

        IconSelect iconSelect(this); //dialog
        for(UINT i=0; i<nIcons; i++)
        {
            qDebug() << i;
            iconSelect.addIcon(QtWin::fromHICON(iconHandles[i])); //fromHICON returns QPixmap
            DestroyIcon(iconHandles[i]);
        }

        iconSelect.exec();
    }
}

图标在对话框中正确加载，但有时会意外导致应用程序崩溃。

知道发生了什么吗？

Documentation on ExtractIconEx

编辑:感谢您快速而有用的回答。以下是我使用 atm 的完整工作代码:

// In my case I have a QString `filePath`
// `QString::toWCharArray` retrieves a non-0-terminated string,
// so append a 0 to `path`
std::vector<WCHAR> path(unsigned(filePath.length())+1); 
filePath.toWCharArray(path.data());
path.at(path.size()-1) = 0;

// Get number of icons in selected file
UINT nIcons = ExtractIconEx(path.data(), -1, nullptr, nullptr, 0);

if(nIcons == 0)
{
    // Try to find associated file that contains icon(s)
    // If found, `path` is replaced with the new path
    WORD index=0;
    DestroyIcon(ExtractAssociatedIcon(GetModuleHandle(nullptr), path.data(), &index));
    // Get number of icons in associated file
    nIcons = ExtractIconEx(path.data(), -1, nullptr, nullptr, 0);
}

if(nIcons > 0)
{
    // Get array of HICONs
    std::vector<HICON> iconHandles(nIcons);
    nIcons = ExtractIconEx(path.data(), 0, iconHandles.data(), nullptr, nIcons);

    for(UINT i=0; i<nIcons; i++) // Using iconHandles.size() is possibly safer,
                                 // but AFAIK nIcons always carries the correct value
    {
        // Use iconHandles[i]
        // In Qt you can use QtWin::fromHICON(iconHandles[i]) to generate a QPixmap
        DestroyIcon(iconHandles[i]);
    }
}

Answer 1

HICON *iconHandles=new HICON;

这里您只分配了一个HICON 对象。如果给定文件中有多个图标，则对 ExtractIconEx() 的下一次调用会通过写入超出分配的内存来创建缓冲区溢出。你已经进入了未定义行为的黑暗世界。

要解决此问题，您可以使用 std::vector像这样:

std::vector<HICON> iconHandles(nIconsCheck); 
const UINT nIcons = ExtractIconEx(path, 0, iconHandles.data(), nullptr, iconHandles.size());
iconHandles.resize(nIcons); // Resize to the actual number of icons.

// Instead of: if(nIcons == nIconsCheck && nIcons != unsigned(-1))
if(!iconHandles.empty())
{
    // Use icons
}

这比手动分配有优势，您不需要删除分配的内存。 vector 析构函数将在作用域结束时自动执行此操作。尽管您仍然需要为每个图标句柄调用 DestroyIcon()。