无法正确封送结构中的StringBuilder字段

Question

我已经在p/invoke问题上挣扎了一段时间了。继续得到“尝试读取或写入受保护的内存”。一直如此，我怀疑我的编组有点不对劲。

下面是c签名：

long ft_show(                             /* show file-attributes        */
    const struct ft_admission *admis,     /* I: transfer admission       */
    const struct ft_shwpar    *par,       /* IO: parameter-list          */
    struct ft_fileinfo        *info,      /* O: requested information    */
    struct ft_err             *errorinfo, /* O: error information        */
    void                      *options    /* I: options                  */
    );

下面是相关的结构(在c中)

struct ft_admission
{
    char    *remsys;
    char    *remadmis;
    char    *remaccount;
    char    *rempasswd;
};

struct ft_shwpar
{
    int                shwparvers;
    char               *fn;
    char               *mgmtpasswd;
    char               *fud;
    int                fudlen;
};

struct ft_fileinfo
{
    int             ftshowivers;
    char            fn[INFO_FN_LEN];
    enum ft_ftype   filetype;
    enum ft_charset charset;
    enum ft_rform   recordform;
    long            recsize;
    enum ft_available availability;
    int             access;
    char            account[ACC_LEN];
    long            size;
    long            maxsize;
    char            legalqual[LQ_LEN];
    char            cre_user[USER_LEN];
    long            cre_date;
    char            mod_user[USER_LEN];
    long            mod_date;
    char            rea_user[USER_LEN];
    long            rea_date;
    char            atm_user[USER_LEN];
    long            atm_date;
    long long       fsize;
    long long       fmaxsize;
};

struct ft_err
{
    long    main;
    long    detail;
    long    additional;
};

struct ft_options
{                                                                       
    int ftoptsvers;
    int ftapivers;
};

我曾尝试创建c#结构和调用，如下所示：

[DllImport("ftapi.dll", EntryPoint = "ft_showdir")]
private static extern long ft_showdir(ft_admission admis, ref ft_shwpar par, ft_fileinfo[] buf, int bufsize, ref ft_err errorinfo, ft_options options);

    public struct ft_admission
    {
        public String remsys;
        public String remadmis;
        public String remaccount;
        public String rempasswd;
    };
    public struct ft_shwpar
    {
        public int shwparvers;
        public String fn;
        public String mgmtpasswd;
        public IntPtr fud;
        public int fudlen;
    };
    [StructLayout(LayoutKind.Sequential, Size = 1464, CharSet = CharSet.Ansi), Serializable]
    public struct ft_fileinfo
    {
        public int ftshowivers;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 257)]
        public String fn;
        public ft_ftype filetype;
        public ft_charset charset;
        public ft_rform recordform;
        public long recsize;
        public ft_available availability;
        public int access;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 65)]
        public String account;
        public long size;
        public long maxsize;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 81)]
        public String legalqual;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 68)]
        public String cre_user;
        public long cre_date;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 68)]
        public String mod_user;
        public long mod_date;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 68)]
        public String rea_user;
        public long rea_date;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 68)]
        public String atm_user;
        public long atm_date;
        public long fsize;
        public long fmaxsize;
    };
    public struct ft_err
    {
        public long main;
        public long detail;
        public long additional;
    }
    public struct ft_options
    {
        public int ftoptsvers;
        public int ftapivers;
    };

我已经在另一个调用中成功地使用了ft_err和ft_options结构，所以我认为它们被正确地编组了。

我认为问题出在ft_fileinfo结构上。我想在其中使用StringBuilder，但框架中存在一个错误，导致无法正确封送结构中的StringBuilder。我已经尝试了这里描述的变通方法：http://support.microsoft.com/kb/327109，但没有成功。

下面是我尝试访问的api文档中提供的代码片段(删除了一些代码，因为它只用于将信息打印到屏幕上)：

/* sample3.c     File management requests                    */
/*************************************************************/
static const char Sccsid[] = "@(#)sample3.c   2.33 2009/03/25";
/*************************************************************

  Program call: sample3 <directory>

 *************************************************************/
/*   Include Files                                           */
/*************************************************************/
#include <stdio.h>       /* printf()                         */
#include <stdlib.h>      /* exit()                           */
#include <string.h>      /* strcat(), strcpy()               */
#include <ftapi.h>

/*************************************************************/
/*                Local Constants and Macros                 */
/*************************************************************/
#define BUFSIZE 200      /* number of ft_fileinfo structures */
                         /* in output buffer                 */

/*************************************************************/
/*               Local Functions Declarations                */
/*************************************************************/
static void error_print(struct ft_err *, char *);
static void printinfo(struct ft_fileinfo *info); 

int main (int argc, char *argv[])
{
    int i;                     /* Some local counter         */
    int count;                 /* Number of files            */
    char remotesys[201];       /* Address of remote systems  */
    char remoteadm[68];        /* Transfer admission         */
    char fud[STAT_FUD_LEN];    /* Further details            */
    struct ft_err errorinfo;   /* Error information          */
    struct ft_admission admis; /* Admission parameters       */
    struct ft_shwpar par;      /* Show directory parameters  */
    struct ft_options opt;     /* Options                    */
    struct ft_fileinfo buf[BUFSIZE]; /* Output buffer        */

    /* Check program arguments                               */
    if (argc != 2)
    {
        printf("Call: %s <directory>\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    /* Initialize ft_transpar structure                      */
    memset(&par, 0, sizeof(par));
    /* Set version of the parameter list                     */
    par.shwparvers  = FT_SPARV2;
    /* Set the name of the remote directory                  */
    par.fn = argv[1];
    /* Set buffer and buffer length for the further details  */
    par.fud = fud;               
    par.fudlen = sizeof(fud);      
    /* Set version of the ft_fileinfo structure in the       */
    /* output buffer. The version in the first structure     */
    /* is valid for all structtures in the output buffer.    */
    buf[0].ftshowivers = FT_SHOWIV2;

    /* Get the name/address of the remote system and the     */
    /* transfer admission                                    */
    printf("Enter name of remote system: ");
    scanf("%s", remotesys);
    printf("Input transfer admission to remote system: ");
    scanf("%s", remoteadm);
    admis.remsys     = remotesys;
    admis.remadmis   = remoteadm;
    admis.remaccount = NULL;
    admis.rempasswd  = NULL;

    /* Prepare the options structure                         */
    opt.ftoptsvers = FT_OPTSV1;
    opt.ftapivers = FT_APIV2; 

    /* Read the contents of the remote directory             */
    count = ft_showdir(&admis, &par, buf, BUFSIZE, &errorinfo,
                       &opt);
    if (count == -1) 
    {   
        /* Error                                             */
        error_print(&errorinfo, par.fud); 
    }

    /* Display result of request                             */
    printf("There are %d entries in remote directory %s\n",
           count, argv[1]);

    /* If the output range was not large enough for all      */
    /* the information, only the data in the buffer is       */
    /* displayed                                             */
    if (count > BUFSIZE)
        count = BUFSIZE;
    for (i = 0; i < count; i++)
         printinfo(&buf[i]);
    return(0);
}

有人能帮我在C#中实现同样的效果吗？甚至解释为什么必须这样，这样我们都可以从中学到一些东西:)

谢谢!

Answer 1

好了，我想通了。

当查看函数的c声明时，我们可以看到所有的参数都是通过引用或通过指针发送的。所以我只是修改了pinvoke声明，这样所有的参数都是ref。

[DllImport("ftapi.dll", EntryPoint = "ft_showdir", CallingConvention = CallingConvention.Cdecl)]
private static extern Int32 ft_showdir(ref ft_admission admis, ref ft_shwpar par, ref ft_fileinfo[] buf, int bufsize, ref ft_err errorinfo, ref ft_options options);

Answer 2

看起来您在DllImport属性中的ft_fileinfo之前缺少引用。我用下面的剪辑重现了你的问题。在C++中定义入口点：

    // OneEntryPoint.cpp : Defines the exported functions for the DLL application.
//

#include "stdafx.h"
#include <stdio.h>
extern "C"
{
    struct AStruct
    {
        char     fn[11];
    };

    __declspec(dllexport) void AnEntry(AStruct* someStruct) 
    {
        printf("A character %c", someStruct->fn[255]); 
    }
}

并在C#中重现调用：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.InteropServices;

namespace ConsoleApplication2
{

    public struct AStruct
    {
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 255)]
        public string fn; 
    }


    class Program
    {
        [DllImport("OneEntryPoint", CallingConvention = CallingConvention.Cdecl)]
         static extern void AnEntry(AStruct somestruct); 


        static void Main(string[] args)
        {
            try
            {
                AStruct fred;
                fred.fn = "hello world";
                Program.AnEntry(fred);
                Console.WriteLine("Done");
            }
            catch (Exception e)
            {
                Console.WriteLine(e.Message);
            }
        }
    }

运行此命令，您将获得一个AccessViolationException (尝试读\写受保护的内存)。把ref放进去，结构就被正确地编组了，没有错误。