将C#多维数组传递给C ++ [英] Passing C# Multidimensional Array to C++
问题描述
// C ++
命名空间
{
公共 参考 class Class1
{
公共:
静态 无效测试( double ** a ， int nRow， int nCol)
{
// 使用2D数组进行操作.
}
};
}
// ========================= ================================
// C#
使用
私有 无效 button1_Click(对象发件人，EventArgs e)
{
double [，] a = 新 double [ 4 ， 3 ]；
a [ 0 ， 0 ] = 1 ; a [ 1 ， 0 ] = 1 ; a [ 2 ， 0 ] = 1 ; a [ 3 ， 0 ] = 0 ;
a [ 0 ， 1 ] = 2 ; a [ 1 ， 1 ] = 1 ; a [ 2 ， 1 ] = 1 ; a [ 3 ， 1 ] = 1 ;
a [ 0 ， 2 ] = 1 ; a [ 1 ， 2 ] = 2 ; a [ 2 ， 2 ] = 1 ; a [ 3 ， 2 ] = 15 ;
不安全
{
已修复(双** ppa = a)// 什么正确的语法是什么?
{
Class1.Test(ppa，a.GetLength( 0 )，a.GetLength( 1 ));
}
}
}
// ++++++++++++++++++++++++++ +++++++++++++++++++++++++++++++++++
C#语法fixed (double** ppa = a)在VS2010 C#中生成了以下错误消息.
错误1无法将类型double *隐式转换为double **.存在显式转换(您是否缺少演员表?)
将C#部分中生成的2D数组传递到C ++ ref类的正确方法是什么?指向本机代码中的指针的指针.您可以将二维数组转换为双锯齿数组(数组数组)，然后将其转换为指向指针的指针，然后将其传递给C ++.
但是，这里一个更重要的问题是，为什么您需要完全执行此操作.您的C ++类是托管类，可以轻松地处理托管数组(包括二维数组).那么，您需要使用指针做什么呢?
>>你能告诉我如何
这是我几年前写的文章:
http://www.codeproject.com/KB/mcpp/cppcliarrays.aspx [ ^ ]
向下滚动到标题为使用本机指针直接操作CLI数组"的部分，然后向下滚动至第二小节以本地方式访问锯齿状的数组".您可能需要进行一些更改以适合您的特定需求，但是该示例将告诉您您需要做什么.
整个要点是避免在C#中执行不安全的代码.将托管类型(2-d或锯齿状数组)传递给C ++/CLI ref类. C ++/CLI ref类将其转换为本机指针类型并调用本机函数.通常就是这样.
[更新(此评论与回答的东西有点混乱！)]
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这是一个示例，显示了如何将二维数组传递给需要指针的本地函数.
void Foo( double ** nums， int yLen) { for ( int i = 0 ; i< ; xLen; i ++) { for ( int j = 0 ; j< ; yLen; j ++) { double d = *( double *)(nums [i] + j); } } } int main(...) { array< double，2> ^数字= gcnew array< double，2>( 2 ， 3 )； 数字[ 0 ， 0 ] = 12 . 3 ; 数字[ 0 ， 1 ] = 2 . 1 ; 数字[ 0 ， 2 ] = 4 . 3 ; 数字[ 1 ， 0 ] = 23 . 2 ; 数字[ 1 ， 1 ] = 7 . 7 ; 数字[ 1 ， 2 ] = 17 . 6 ; pin_ptr< double> p1 =& numbers [ 0 ， 0 ]; pin_ptr< double> p2 =& numbers [ 1 ， 0 ]; double * p3 [ 2 ]; p3 [ 0 ] = p1; p3 [ 1 ] = p2; double ** p4 = p3; Foo(p4， 2 ， 3 ); 返回 0 ; }
// C++
namespace whatever
{
public ref class Class1
{
public:
static void Test(double **a, int nRow, int nCol)
{
// Do something with 2D array.
}
};
}
//========================================================
// C#
using whatever
private void button1_Click(object sender, EventArgs e)
{
double[,] a = new double[4, 3];
a[0, 0] = 1; a[1, 0] = 1; a[2, 0] = 1; a[3, 0] = 0;
a[0, 1] = 2; a[1, 1] = 1; a[2, 1] = 1; a[3, 1] = 1;
a[0, 2] = 1; a[1, 2] = 2; a[2, 2] = 1; a[3, 2] = 15;
unsafe
{
fixed (double** ppa = a) // What is the correct syntax?
{
Class1.Test(ppa, a.GetLength(0), a.GetLength(1));
}
}
}
// +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
The C# syntax fixed (double** ppa = a) generated the following error message in VS2010 C#.
Error 1 Cannot implicitly convert type double* to double**. An explicit conversion exists (are you missing a cast?)
What is the correct way to pass the 2D array generated in the C# part over to the C++ ref class?
Unfortunately a managed multi-dimensional array is not equivalent to a pointer to pointer in native code. You could convert your 2-dimensional array into a doubly jagged array (an array of arrays) and then convert that to a pointer to a pointer and then pass that to C++.
But a more important question here is why you need to do this at all. Your C++ class is managed and can easily and trivially handle a managed array (including a 2-d array). So what do you need to resort to pointers for?
>> Would you show me how
This is an article I wrote some years back:
http://www.codeproject.com/KB/mcpp/cppcliarrays.aspx[^]
Scroll down to the section titled "Direct manipulation of CLI arrays using native pointers", and then the 2nd sub-section "Natively accessing a jagged array". You may need to change things just a little to fit your specific needs but that example should tell you what you need to do.
The whole point is to avoid doing the unsafe code in C#. Pass the managed type (2-d or jagged array) to the C++/CLI ref class. The C++/CLI ref class converts this to the native pointer type and calls the native function. That''s how this is typically done.
[Update (this comment vs answer thing is kinda messy!)]
----------------------------------------------------------------
Here''s a sample showing how you can pass a 2-d array to a native function expecting a pointer to pointer.
void Foo(double** nums, int xLen, int yLen) { for (int i=0; i<xLen; i++) { for (int j=0; j<yLen; j++) { double d = *(double*)(nums[i] + j); } } } int main(. . .) { array<double, 2>^ numbers = gcnew array<double, 2>(2,3); numbers[0,0] = 12.3; numbers[0,1] = 2.1; numbers[0,2] = 4.3; numbers[1,0] = 23.2; numbers[1,1] = 7.7; numbers[1,2] = 17.6; pin_ptr<double> p1 = &numbers[0,0]; pin_ptr<double> p2 = &numbers[1,0]; double* p3[2]; p3[0] = p1; p3[1] = p2; double** p4 = p3; Foo(p4, 2, 3); return 0; }
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