c# - EnumJobs返回与Marshal.SizeOF不同的JOB_INFO_1大小

我正在从托管代码（c）调用win32函数enumjobs（http://msdn.microsoft.com/en-us/library/windows/desktop/dd162625(v=vs.85).aspx）。

    [DllImport("Winspool.drv", SetLastError = true, EntryPoint = "EnumJobsA")]
    public static extern bool EnumJobs(
       IntPtr hPrinter,                    // handle to printer object
       UInt32 FirstJob,                // index of first job
       UInt32 NoJobs,                // number of jobs to enumerate
       UInt32 Level,                    // information level
       IntPtr pJob,                        // job information buffer
       UInt32 cbBuf,                    // size of job information buffer
       out UInt32 pcbNeeded,    // bytes received or required
       out UInt32 pcReturned    // number of jobs received
    );

EnumJobs(_printerHandle, 0, 99, 1, IntPtr.Zero, 0, out nBytesNeeded, out pcReturned);

我正在指定级别1以接收作业信息1，但我遇到的问题是，上面的函数返回nbytesneded作为每个结构的240，而Marshal.SizeOf(typeof(JOB_INFO_1))是64个字节，在我运行Marshal.PtrToStructure时会导致内存异常。手动计算结构的字节数得到64，所以对于为什么从函数接收240字节的结构，我有点不知所措，任何洞察都是值得赞赏的。

[StructLayout(LayoutKind.Sequential, Pack = 1, CharSet=CharSet.Unicode)]
public struct JOB_INFO_1
{
    public UInt32 JobId;
    public string pPrinterName;
    public string pMachineName;
    public string pUserName;
    public string pDocument;
    public string pDatatype;
    public string pStatus;
    public UInt32 Status;
    public UInt32 Priority;
    public UInt32 Position;
    public UInt32 TotalPages;
    public UInt32 PagesPrinted;
    public SYSTEMTIME Submitted;
}

最佳答案

64的大小对于JOB_INFO_1来说确实是正确的，但是如果您仔细查看文档，它会谈到一系列结构：

pJob [out]
A pointer to a buffer that receives an array of JOB_INFO_1, JOB_INFO_2, or JOB_INFO_3 structures.

此外，它还写道：
The buffer must be large enough to receive the array of structures and any strings or other data to which the structure members point.
所以除了结构本身之外，这里还有字节用于额外的数据。
解决方案：
填充结构，为下一个结构增加指针并忽略其余字节。
完整示例：

using System;
using System.Diagnostics;
using System.Runtime.InteropServices;
using System.Windows;

namespace WpfApplication3
{
    public partial class MainWindow
    {
        public MainWindow()
        {
            InitializeComponent();
            Loaded += MainWindow_Loaded;
        }

        private void MainWindow_Loaded(object sender, RoutedEventArgs e)
        {
            // Get handle to a printer
            var hPrinter = new IntPtr();
            bool open = NativeMethods.OpenPrinterW("Microsoft XPS Document Writer", ref hPrinter, IntPtr.Zero);
            Debug.Assert(open);

            /* Query for 99 jobs */
            const uint firstJob = 0u;
            const uint noJobs = 99u;
            const uint level = 1u;

            // Get byte size required for the function
            uint needed;
            uint returned;
            bool b1 = NativeMethods.EnumJobsW(
                hPrinter, firstJob, noJobs, level, IntPtr.Zero, 0, out needed, out returned);
            Debug.Assert(!b1);
            uint lastError = NativeMethods.GetLastError();
            Debug.Assert(lastError == NativeConstants.ERROR_INSUFFICIENT_BUFFER);

            // Populate the structs
            IntPtr pJob = Marshal.AllocHGlobal((int) needed);
            uint bytesCopied;
            uint structsCopied;
            bool b2 = NativeMethods.EnumJobsW(
                hPrinter, firstJob, noJobs, level, pJob, needed, out bytesCopied, out structsCopied);
            Debug.Assert(b2);

            var jobInfos = new JOB_INFO_1W[structsCopied];
            int sizeOf = Marshal.SizeOf(typeof (JOB_INFO_1W));
            IntPtr pStruct = pJob;
            for (int i = 0; i < structsCopied; i++)
            {
                var jobInfo_1W = (JOB_INFO_1W) Marshal.PtrToStructure(pStruct, typeof (JOB_INFO_1W));
                jobInfos[i] = jobInfo_1W;
                pStruct += sizeOf;
            }
            Marshal.FreeHGlobal(pJob);

            // do something with your structs
        }
    }

    public class NativeConstants
    {
        public const int ERROR_INSUFFICIENT_BUFFER = 122;
    }

    public partial class NativeMethods
    {
        [DllImport("kernel32.dll", EntryPoint = "GetLastError")]
        public static extern uint GetLastError();
    }

    public partial class NativeMethods
    {
        [DllImport("Winspool.drv", EntryPoint = "OpenPrinterW")]
        [return: MarshalAs(UnmanagedType.Bool)]
        public static extern bool OpenPrinterW([In] [MarshalAs(UnmanagedType.LPWStr)] string pPrinterName,
            ref IntPtr phPrinter, [In] IntPtr pDefault);

        [DllImport("Winspool.drv", EntryPoint = "EnumJobsW")]
        [return: MarshalAs(UnmanagedType.Bool)]
        public static extern bool EnumJobsW([In] IntPtr hPrinter, uint FirstJob, uint NoJobs, uint Level, IntPtr pJob,
            uint cbBuf, [Out] out uint pcbNeeded, [Out] out uint pcReturned);
    }

    [StructLayout(LayoutKind.Sequential)]
    public struct JOB_INFO_1W
    {
        public uint JobId;
        [MarshalAs(UnmanagedType.LPWStr)] public string pPrinterName;
        [MarshalAs(UnmanagedType.LPWStr)] public string pMachineName;
        [MarshalAs(UnmanagedType.LPWStr)] public string pUserName;
        [MarshalAs(UnmanagedType.LPWStr)] public string pDocument;
        [MarshalAs(UnmanagedType.LPWStr)] public string pDatatype;
        [MarshalAs(UnmanagedType.LPWStr)] public string pStatus;
        public uint Status;
        public uint Priority;
        public uint Position;
        public uint TotalPages;
        public uint PagesPrinted;
        public SYSTEMTIME Submitted;
    }

    [StructLayout(LayoutKind.Sequential)]
    public struct SYSTEMTIME
    {
        public ushort wYear;
        public ushort wMonth;
        public ushort wDayOfWeek;
        public ushort wDay;
        public ushort wHour;
        public ushort wMinute;
        public ushort wSecond;
        public ushort wMilliseconds;
    }
}

结果：
作业1：
作业2：
编辑
似乎您需要比我做的更健壮的检查，因为当队列中没有作业时，EnumJobs似乎会返回true。在我的示例中，断言将失败，但这并不意味着代码是错误的；只需确保队列中有一些用于测试函数的作业。

关于c# - EnumJobs返回与Marshal.SizeOF不同的JOB_INFO_1大小，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/26857875/