mysql - 如何在 Visual C++/CLI 中从 MySQL 检索图像

Question

我想使用 Visual C++ 从 MySQL 数据库中检索 LONG BLOB 类型的图像，我在关键事件中尝试这样做

String^ con = L"datasource=localhost;port=3306;username=root;password=root";
    MySqlConnection^ conn = gcnew MySqlConnection(con);
    MySqlCommand^ cmd = gcnew MySqlCommand("select * from test.testphoto where test.testphoto.name=@name",conn);
    MySqlDataReader^ re;
    try {
        conn->Open();
        cmd->Parameters->AddWithValue("@name", "shakira");
        re = cmd->ExecuteReader();
        while (re->Read()) {
            BinaryFormatter^ bf = gcnew BinaryFormatter(); // to convert object to byte array
            MemoryStream^ ms = gcnew MemoryStream();
            bf->Serialize(ms, re->GetValue(1));
            pictureBox1->Image = gcnew Bitmap(ms);
            MessageBox::Show("Excute");
        }
    }
    catch (Exception ^e) {
        MessageBox::Show(e->Message, "Error");
    }
    conn->Close();

这里的问题是我收到错误

parameter is not valid
Update
i try this now and same Error parameter is not valid please any help

String^ con = L"datasource=localhost;port=3306;username=root;password=kapookingkong";
    MySqlConnection^ conn = gcnew MySqlConnection(con);
    MySqlCommand^ cmd = gcnew MySqlCommand("select * from test.testphoto where test.testphoto.name='shakira'",conn);
    MySqlDataReader^ re;
    try {
        conn->Open();
        re = cmd->ExecuteReader();
        re->Read();
        BinaryFormatter^ fe = gcnew BinaryFormatter();
        MemoryStream^ ms = gcnew MemoryStream();
        fe->Serialize(ms, re["photo"]);
        array<Byte>^ arr = ms->ToArray();
        MemoryStream^ ms2 = gcnew MemoryStream(arr);
        pictureBox1->Image = Image::FromStream(ms2);
    }
    catch (Exception ^e) {
        MessageBox::Show(e->Message, "Error");
    }
    conn->Close();

第三次尝试这次索引超出数组范围请提供任何帮助
这解决了我选择错误的列

String^ con = L"datasource=localhost;port=3306;username=root;password=root";
    MySqlConnection^ conn = gcnew MySqlConnection(con);
    MySqlCommand^ cmd = gcnew MySqlCommand("select photo from test.testphoto where test.testphoto.name='amr'",conn);
    MySqlDataReader^ re;
    try {
        conn->Open();
        re = cmd->ExecuteReader();
        array<Byte>^ arr;
        while (re->Read())
        {
            long long l = re->GetBytes(1, 0, nullptr, 0, 0);
            arr = gcnew array<Byte>(l);
            re->GetBytes(1, 0, arr, 0, l);
        }
        pictureBox1->Image = Image::FromStream(gcnew MemoryStream(arr));
        pictureBox1->Refresh();
    }
    catch (Exception ^e) {
        MessageBox::Show(e->Message, "Error");
    }
    conn->Close();

我从 C# 代码中获取此代码，我尝试对其进行修改，以便可以在 C++ 中使用它，但我没有找到任何在 Visual C++ 中从 MySQL 检索图像的答案

注意:我使用的是 Visual C++ 2015

Answer 1

BinaryFormatter^ bf = gcnew BinaryFormatter();//将对象转换为字节数组

该对象包含一个字节数组。将包含字节数组的对象转换为字节数组会产生原始字节数组以外的结果。您可以通过创建一个字节数组、序列化它，然后检查内存流的内容(现在会更大)的简单示例来验证这一点

我认为您需要在阅读器上使用 GetBytes() 。您可以阅读https://msdn.microsoft.com/en-us/library/87z0hy49%28v=vs.110%29.aspx了解更多信息和 MySqlDataReader GetBytes buffer issue...