为什么访问非托管内存会导致System.AccessViolationException? [英] Why does accessing unmanaged memory cause a System.AccessViolationException?
问题描述
我正在尝试使用 XGBoost的 dll(libxgboost.dll)创建一个DMatrix(其中就像一个二维数组),并得到它有多少列。它运行正常,直到在$ code> int cols = ... 行在下面的代码中抛出一个 System.AccessViolationException
I'm trying to use XGBoost's dll (libxgboost.dll) to create a DMatrix (which is like a 2D array) and get how many columns it has. It runs fine until it throws a System.AccessViolationException
at the int cols = ...
line in the code below:
using System;
using System.Runtime.InteropServices;
namespace basicXgboost
{
class Program
{
[DllImport("../../libs/libxgboost.dll", CharSet = CharSet.Auto)]
public static extern int XGDMatrixCreateFromFile([MarshalAs(UnmanagedType.LPStr)] string file, int silent, IntPtr outputPtr);
[DllImport("../../libs/libxgboost.dll", CharSet = CharSet.Auto)]
public static extern int XGDMatrixNumCol(IntPtr dmatrixPtr, IntPtr dmatrixColumnsPtr);
static void Main(string[] args)
{
IntPtr dmatrixPtr = Marshal.AllocHGlobal(1000000);
IntPtr dmatrixColumnsPtr = Marshal.AllocHGlobal(10);
int result = XGDMatrixCreateFromFile("../../libs/test.txt", 0, dmatrixPtr);
int cols = XGDMatrixNumCol(dmatrixPtr, dmatrixColumnsPtr);
Marshal.FreeHGlobal(dmatrixPtr);
Marshal.FreeHGlobal(dmatrixColumnsPtr);
}
}
}
为什么访问非托管内存分配与 XGDMatrixNumCol(dmatrixPtr,dmatrixColumnsPtr)
导致一个 System.AccessViolationException
?
Why does accessing unmanaged memory allocated with XGDMatrixNumCol(dmatrixPtr, dmatrixColumnsPtr)
cause a System.AccessViolationException
?
一种可能性是我使用pinvoke不正确的这些功能。以下是我使用的每个dll函数的定义:
One possibility might be that I'm using pinvoke incorrectly for these functions. Below are the definitions for each dll function I use:
/*!
* \brief load a data matrix
* \param fname the name of the file
* \param silent whether print messages during loading
* \param out a loaded data matrix
* \return 0 when success, -1 when failure happens
*/
XGB_DLL int XGDMatrixCreateFromFile(const char *fname,
int silent,
DMatrixHandle *out);
/*!
* \brief get number of columns
* \param handle the handle to the DMatrix
* \param out The output of number of columns
* \return 0 when success, -1 when failure happens
*/
XGB_DLL int XGDMatrixNumCol(DMatrixHandle handle,
bst_ulong *out);
这里是我的项目的回购。我使用的是Visual Studio Enterprise 2015。它以Windows 10 Pro(64位)的Debug模式(针对x64)内置。可以找到x64二进制文件libxgboost.dll 这里。虽然链接的repo确实包含一个libxgboost.dll的副本。
Here is the repo for my project. I'm using Visual Studio Enterprise 2015 . It's built in "Debug" mode (targeting x64) on Windows 10 Pro (64-bit). x64 binaries for libxgboost.dll can be found here. Although the linked repo does contain a copy of libxgboost.dll.
推荐答案
这是解决方案,感谢 NineBerry的答案。
using System;
using System.Runtime.InteropServices;
namespace basicXgboost
{
class Program
{
[DllImport("../../libs/libxgboost.dll", CharSet = CharSet.Auto)]
public static extern int XGDMatrixCreateFromFile([MarshalAs(UnmanagedType.LPStr)] string file, int silent, out IntPtr outputPtr);
[DllImport("../../libs/libxgboost.dll", CharSet = CharSet.Auto)]
public static extern int XGDMatrixNumCol(IntPtr dmatrixPtr, out ulong dmatrixColumnsPtr);
static void Main(string[] args)
{
IntPtr dmatrixPtr;
ulong dmatrixColumns;
int result = XGDMatrixCreateFromFile("../../libs/test.txt", 0, out dmatrixPtr);
int cols = XGDMatrixNumCol(dmatrixPtr, out dmatrixColumns);
}
}
}
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