从C#程序调用外部DLL函数(QPDF库)时的访问冲突

Question

构建环境: Visual 2019，Windows应用程序，.net 4.7.2

我试图使用QPDF .dll库来读取、加密和输出PDF文件。有关DLL头文件，请参见这里，该文件将所有公开函数作为声明列出。

备注：

• QPDF_BOOL是'int‘的类型 qpdf_r3_print_e是一个整数枚举，所以我认为它也是'int‘。

我可以成功地初始化QPDF库，读取该文件，并通过调用必要的函数将其输出到一个新文件，但是当我在初始化和成功读取文件之后添加对qpdf_set_r6_encryption_parameters2()函数的调用时，它会引发访问冲突。这可能是因为参数类型不正确，但我已经尽可能地阅读了QPDF代码来使用正确的类型。

下面是我的DllImport代码中的C#：(所有DllImport行都遵循这个建议 )

[DllImport("qpdf28.dll", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
        static extern void qpdf_set_r6_encryption_parameters2(
            IntPtr qpdf, 
            [MarshalAs(UnmanagedType.LPStr)] string user_password,
            [MarshalAs(UnmanagedType.LPStr)] string owner_password,
            int allow_accessibility,
            int allow_extract,
            int allow_assemble,
            int allow_annotate_and_form,
            int allow_form_filling,
            int allow_modify_other,
            int print,
            int encrypt_metadata

            );

下面是C#代码后面的函数调用：

qpdf_set_r6_encryption_parameters2(qpdf,
                    txtPassword.Text,
                    txtPassword.Text,
                    0, 0, 0, 0, 0, 0,
                     0,
                     0
                    );

我很确定参数数据类型在某个地方是错误的，但我没有看到。谢谢你的指点！

更新:这是我试图运行的完整代码，如果这有帮助的话。注意，如果我禁用加密行，代码将完美地工作:它写入一个新的PDF文件，其中包含与输入PDF相同的信息。

namespace testqpdf
{
    public partial class Form1 : Form
    {
        enum qpdf_r3_print_e
        {
            qpdf_r3p_full = 0,
            qpdf_r3p_low = 1,
            qpdf_r3p_none = 2
        }

        [DllImport("qpdf28.dll", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
        static extern IntPtr qpdf_init();

        [DllImport("qpdf28.dll", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
        static extern void qpdf_cleanup(ref IntPtr qpdfData);

        [DllImport("qpdf28.dll", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
        static extern int qpdf_read(IntPtr qpdfdata, [MarshalAs(UnmanagedType.LPStr)] string fileName, IntPtr password);

        [DllImport("qpdf28.dll", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
        static extern void qpdf_set_object_stream_mode(IntPtr qpdf, int mode);

        [DllImport("qpdf28.dll", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
        static extern void qpdf_set_qdf_mode(IntPtr qpdf, int value);

        [DllImport("qpdf28.dll", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
        static extern int qpdf_init_write(IntPtr qpdf, [MarshalAs(UnmanagedType.LPStr)] string fileName);

        [DllImport("qpdf28.dll", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
        static extern int qpdf_write(IntPtr qpdf);

        [DllImport("qpdf28.dll", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
        static extern void qpdf_set_r6_encryption_parameters2(
            IntPtr qpdf, 
            [MarshalAs(UnmanagedType.LPStr)] string user_password,
            [MarshalAs(UnmanagedType.LPStr)] string owner_password,
            int allow_accessibility,
            int allow_extract,
            int allow_assemble,
            int allow_annotate_and_form,
            int allow_form_filling,
            int allow_modify_other,
            int print,
            int encrypt_metadata

            );




        public Form1()
        {
            InitializeComponent();
        }

        private void btnGo_Click(object sender, EventArgs e)
        {
            IntPtr qpdf = qpdf_init();

            int result = qpdf_read(qpdf, txtInput.Text, /* password */ IntPtr.Zero);

            Console.WriteLine("Read PDF file " + txtInput.Text + ", result = " + result.ToString());

            if (chkEncrypt.Checked)
            {
                qpdf_set_r6_encryption_parameters2(qpdf,
                    null,
                    null,
                    0, 0, 0, 0, 0, 0,
                     0,
                     0

                    );
            }


            result = qpdf_init_write(qpdf, txtOutput.Text);

            Console.WriteLine("Write PDF file " + txtOutput.Text + ", result = " + result.ToString());

            result = qpdf_write(qpdf);

            qpdf_cleanup(ref qpdf);
        }
    }
}

Answer 1

试试这个：

[DllImport("qpdf29.dll", CharSet = CharSet.Unicode, CallingConvention = CallingConvention.Cdecl)]
static extern IntPtr qpdf_init();

[DllImport("qpdf29.dll", CharSet = CharSet.Unicode, CallingConvention = CallingConvention.Cdecl)]
static extern void qpdf_cleanup(ref IntPtr qpdfData);

[DllImport("qpdf29.dll", CharSet = CharSet.Unicode, CallingConvention = CallingConvention.Cdecl)]
static extern int qpdf_read(IntPtr qpdfdata, [MarshalAs(UnmanagedType.LPStr)] string fileName, IntPtr password);

[DllImport("qpdf29.dll", CharSet = CharSet.Unicode, CallingConvention = CallingConvention.Cdecl)]
static extern void qpdf_set_qdf_mode(IntPtr qpdf, int value);

[DllImport("qpdf29.dll", CharSet = CharSet.Unicode, CallingConvention = CallingConvention.Cdecl)]
static extern int qpdf_init_write(IntPtr qpdf, [MarshalAs(UnmanagedType.LPStr)] string fileName);

[DllImport("qpdf29.dll", CharSet = CharSet.Unicode, CallingConvention = CallingConvention.Cdecl)]
static extern int qpdf_write(IntPtr qpdf);


IntPtr pdfData = qpdf_init();
qpdf_read(pdfData, @"C:\source file.pdf", IntPtr.Zero);
qpdf_init_write(pdfData, @"C:destination file.pdf");
qpdf_set_qdf_mode(pdfData, 1);
qpdf_write(pdfData);
qpdf_cleanup(ref pdfData);