blocks|key|232428|text|您选择的PInvoke签名有两个问题。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|232429|第一个问题很容易解决。您对unsigned+long的翻译有误。在C中，unsigned+long通常只有4个字节。您选择了8字节的C#类型long。将C#代码更改为使用uint可以解决此问题。|offset|length|style|CODE|232430|第二个更难一些。正如Tergiver指出的那样，CLR+Marshaller只支持返回位置的结构(如果它是blittable的)。Blittable是一种奇妙的说法，它在本机代码和托管代码中具有完全相同的内存表示形式。您选择的结构定义不是blittable，因为它有一个嵌套数组。|232431|但是，如果您还记得PInvoke是一个非常简单的过程，那么这个问题是可以解决的。CLR+Marshaller实际上只需要您用您的类型和pinvoke方法的签名回答两个问题|232432|232433|我要复制多少字节？|unordered-list-item|232434|它们需要朝哪个方向移动？|232435|232436|在本例中，字节数为sizeof(unsigned+long)+%2B+128+==+132。所以我们需要做的就是建立一个托管类型，它是blittable的，大小为132字节。最简单的方法是定义一个blob来处理数组部分|232437|[StructLayout(LayoutKind.Sequential,+Size+=+128)]
struct+Blob
{
+++//+Intentionally+left+empty.+It's+just+a+blob
}|code-block|syntax|javascript|232438|这是一个没有成员的结构，对编组程序来说，它的大小是128字节(另外，它是blittable!)。现在，我们可以轻松地将Frame结构定义为uint和此类型的组合|232439|struct+Frame
{
++++public+int+Identifier;
++++public+Blob+NameBlob;
++++...
}|232440|现在我们有了一个大小为132字节的blittable类型。这意味着它可以很好地使用您定义的GetFrame签名|232441|剩下的唯一部分就是让您访问该名称的实际char[]。这有点棘手，但可以通过一些法警魔法来解决。|232442|public+string+GetName()
{
++++IntPtr+ptr+=+IntPtr.Zero;
++++try
++++{
++++++++ptr+=+Marshal.AllocHGlobal(128);
++++++++Marshal.StructureToPtr(NameBlob,+ptr,+false);
++++++++return+Marshal.PtrToStringAnsi(ptr,+128);
++++}
++++finally
++++{
++++++++if+(ptr+!=+IntPtr.Zero)+
++++++++{
++++++++++++Marshal.FreeHGlobal(ptr);
++++++++}
++++}
}|232443|注意:我不能评论调用约定部分，因为我不熟悉GetFrame应用程序接口，但我肯定会检查这一点。|232444|entityMap^0|0|D|D|10|D|1Y|4|2D|4|0|0|0|0|0|0|0|9|Y|0|0|1N|5|1X|4|0|0|19|8|0|J|6|0|0|L|8|0^^$0|@$1|2|3|4|5|6|7|1D|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1E|8|@$D|1F|E|1G|F|G]|$D|1H|E|1I|F|G]|$D|1J|E|1K|F|G]|$D|1L|E|1M|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|1N|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|1O|8|@]|9|@]|A|$]]|$1|L|3|-4|5|6|7|1P|8|@]|9|@]|A|$]]|$1|M|3|N|5|O|7|1Q|8|@]|9|@]|A|$]]|$1|P|3|Q|5|O|7|1R|8|@]|9|@]|A|$]]|$1|R|3|-4|5|6|7|1S|8|@]|9|@]|A|$]]|$1|S|3|T|5|6|7|1T|8|@$D|1U|E|1V|F|G]]|9|@]|A|$]]|$1|U|3|V|5|W|7|1W|8|@]|9|@]|A|$X|Y]]|$1|Z|3|10|5|6|7|1X|8|@$D|1Y|E|1Z|F|G]|$D|20|E|21|F|G]]|9|@]|A|$]]|$1|11|3|12|5|W|7|22|8|@]|9|@]|A|$X|Y]]|$1|13|3|14|5|6|7|23|8|@$D|24|E|25|F|G]]|9|@]|A|$]]|$1|15|3|16|5|6|7|26|8|@$D|27|E|28|F|G]]|9|@]|A|$]]|$1|17|3|18|5|W|7|29|8|@]|9|@]|A|$X|Y]]|$1|19|3|1A|5|6|7|2A|8|@$D|2B|E|2C|F|G]]|9|@]|A|$]]|$1|1B|3|-4|5|6|7|2D|8|@]|9|@]|A|$]]]|1C|$]]

There are two problems with the PInvoke signature that you've chosen.

The first is easy to fix. You have a mistranslation of <code>unsigned long</code>. In C an <code>unsigned long</code> is typically only 4 bytes. You chose the C# type <code>long</code> which is 8 bytes. Changing the C# code to use <code>uint</code> will fix this.

The second is a bit harder. As Tergiver pointed out the CLR Marshaller only supports a struct in the return position if it's blittable. Blittable is a fancy way of saying that it has the exact same memory representation in native and managed code. The struct definition you've chosen isn't blittable because it has a nested array. 

This can be worked around though if you remember that PInvoke is a very simple process. The CLR Marshaller really just needs you to answer 2 questions with the signature of your types and pinvoke methods

<ul>
<li>How many bytes am I copying? </li>
<li>In which direction do they need to go?</li>
</ul>

In this case the number of bytes is <code>sizeof(unsigned long) + 128 == 132</code>. So all we need to do is build up a managed type that is blittable and has a size of 132 bytes. The easiest way to do this is to define a blob to handle the array portion

<pre><code>[StructLayout(LayoutKind.Sequential, Size = 128)]
struct Blob
{
 // Intentionally left empty. It's just a blob
}
</code></pre>

This is a struct with no members that will appear to the marshaller as having a size of 128 bytes (and as a bonus it's blittable!). Now we can easily define the <code>Frame</code> structure as a combination of an <code>uint</code> and this type

<pre><code>struct Frame
{
 public int Identifier;
 public Blob NameBlob;
 ...
}
</code></pre>

Now we have a blittable type with a size the marshaller will see as 132 bytes. This means it will work just fine with the <code>GetFrame</code> signature you've defined

The only part left is giving you access to the actual <code>char[]</code> for the name. This is a bit tricky but can be solved with a bit of marshal magic. 

<pre><code>public string GetName()
{
 IntPtr ptr = IntPtr.Zero;
 try
 {
 ptr = Marshal.AllocHGlobal(128);
 Marshal.StructureToPtr(NameBlob, ptr, false);
 return Marshal.PtrToStringAnsi(ptr, 128);
 }
 finally
 {
 if (ptr != IntPtr.Zero) 
 {
 Marshal.FreeHGlobal(ptr);
 }
 }
}
</code></pre>

Note: I can't comment on the calling convention portion because I'm unfamiliar with the <code>GetFrame</code> API but that's something i would definitely check on.

blocks|key|3102384|text|问题是本机函数返回一个非blittable类型作为返回值。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3102385|http://msdn.microsoft.com/en-us/library/ef4c3t39.aspx|offset|length|3102386|P/Invoke不能将非blittable类型作为返回值。|3102387|您不能p/调用该方法。[EDIT这实际上是可能的，请参见]|style|BOLD|3102388|通过值返回132个字节不是一个好主意。如果这个本机代码是你的，我会修复它。你可以通过分配132个字节并返回一个指针来修复它。然后添加一个FreeFrame方法来释放该内存。现在可以p/调用它了。|3102389|或者，您可以将其更改为接受指向它将填充的帧内存的指针。|3102390|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|1H|0|0|0|C|4|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|X|8|@]|9|@$D|Y|E|Z|1|10]]|A|$]]|$1|F|3|G|5|6|7|11|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|12|8|@$D|13|E|14|J|K]]|9|@]|A|$]]|$1|L|3|M|5|6|7|15|8|@]|9|@]|A|$]]|$1|N|3|O|5|6|7|16|8|@]|9|@]|A|$]]|$1|P|3|-4|5|6|7|17|8|@]|9|@]|A|$]]]|Q|$R|$5|S|T|U|A|$V|C]]]]

The problem is that the native function returns a non-blittable type as a return value.

<a href="http://msdn.microsoft.com/en-us/library/ef4c3t39.aspx" rel="nofollow noreferrer">http://msdn.microsoft.com/en-us/library/ef4c3t39.aspx</a>

P/Invoke cannot have non-blittable types as a return value.

You cannot p/Invoke that method. [EDIT It is actually possible, see <a href="https://stackoverflow.com/questions/10320502/c-sharp-calling-c-function-that-returns-struct-with-fixed-size-char-array/10320690#10320690">JaredPar's answer</a>]

Returning 132 bytes by value is a bad idea. If this native code is yours, I would fix it. You can fix it by allocating the 132 bytes and returning a pointer. Then add a FreeFrame method to release that memory. Now it can be p/Invoked.

Alternately, you could change it to accept a pointer to the Frame memory that it will fill in.

blocks|key|230128|text|JaredPar的另一个选择是利用C#固定大小的缓冲区特性。然而，这确实需要您打开该设置以允许不安全代码，但它避免了具有2个结构。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|230129|class+Program
{
++++private+const+int+SIZE+=+128;

++++unsafe+public+struct+Frame
++++{
++++++++public+uint+Identifier;
++++++++public+fixed+byte+Name[SIZE];
++++}

++++[DllImport("PinvokeTest2.DLL",+CallingConvention+=+CallingConvention.Cdecl,+CharSet+=+CharSet.Ansi)]
++++private+static+extern+Frame+GetFrame(int+index);

++++static+unsafe+string+GetNameFromFrame(Frame+frame)
++++{
++++++++//Option+1:+Use+if+the+string+in+the+buffer+is+always+null+terminated
++++++++//return+Marshal.PtrToStringAnsi(new+IntPtr(frame.Name));

++++++++//Option+2:+Use+if+the+string+might+not+be+null+terminated+for+any+reason,
++++++++//like+if+were+128+non-null+characters,+or+the+buffer+has+corrupt+data.

++++++++return+Marshal.PtrToStringAnsi(new+IntPtr(frame.Name),+SIZE).Split('\0')[0];
++++}

++++static+void+Main()
++++{
++++++++Frame+a+=+GetFrame(0);
++++++++Console.WriteLine(GetNameFromFrame(a));
++++}
}|code-block|syntax|javascript|230130|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Another option to JaredPar's is to utilize the C# fixed size buffer feature. This does however require you to turn on the setting to allow unsafe code, but it avoids having 2 structs.

<pre><code>class Program
{
 private const int SIZE = 128;

 unsafe public struct Frame
 {
 public uint Identifier;
 public fixed byte Name[SIZE];
 }

 [DllImport("PinvokeTest2.DLL", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Ansi)]
 private static extern Frame GetFrame(int index);

 static unsafe string GetNameFromFrame(Frame frame)
 {
 //Option 1: Use if the string in the buffer is always null terminated
 //return Marshal.PtrToStringAnsi(new IntPtr(frame.Name));

 //Option 2: Use if the string might not be null terminated for any reason,
 //like if were 128 non-null characters, or the buffer has corrupt data.

 return Marshal.PtrToStringAnsi(new IntPtr(frame.Name), SIZE).Split('\0')[0];
 }

 static void Main()
 {
 Frame a = GetFrame(0);
 Console.WriteLine(GetNameFromFrame(a));
 }
}
</code></pre>

So, there have been many variants of this question, and after looking at several I still can't figure it out.

This is the C code:

<pre><code>typedef struct
{
unsigned long Identifier;
char Name[128];
} Frame;

Frame GetFrame(int index);
</code></pre>

This is the C# code:

<pre><code>struct Frame
{
 public ulong Identifier;
 [MarshalAs(UnmanagedType.ByValArray, ArraySubType = UnmanagedType.I1, SizeConst = 128)]
 public char[] Name;
}

[DllImport("XNETDB.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Ansi)]
private static extern Frame GetFrame(int index);
</code></pre>

This is the last attempt I tried in C#, and it seems pretty logical, but I get the error "Method's signature is not PInvoke compatible." So, I'm kind of lost on what to try next. Any help is appreciated.

Thanks,
Kevin

Updated Kevin added this as an edit to my answer

I should instead change my C code:

<pre><code>void GetFrame(int index, Frame * f);
</code></pre>

and use instead for C#:

<pre><code>struct Frame
{
 public uint Identifier;
 [MarshalAsAttribute(UnmanagedType.ByValTStr, SizeConst = 128)]
 public string Name;
}

[DllImport("XNETDB.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Ansi)]
private static extern void GetFrame(int index, ref Frame f);
</code></pre>

C# calling C function that returns struct with fixed size char array

所以，这个问题有很多变体，在看了几个之后，我仍然无法理解。这是C代码：typedef struct{unsigned long Identifier;char Name[128];} Frame;Frame GetFrame(int index);这是C#代码：struct Frame{    public ulong...

问C#调用返回具有固定大小字符数组的结构的C函数
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