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POUnmarshalling a Struct containing an array of structs
 

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  1. POUnmarshalling a Struct containing an array of structs
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    <p>I'm trying to get back this struct from a native C library through P/Invoke: </p> <pre><code>struct ndb_mgm_cluster_state { int no_of_nodes; struct ndb_mgm_node_state node_states[1]; }; </code></pre> <p>where <code>ndb_mgm_node_state</code> is:</p> <pre><code>struct ndb_mgm_node_state { int node_id; enum ndb_mgm_node_type node_type; enum ndb_mgm_node_status node_status; int start_phase; int dynamic_id; int node_group; int version; int connect_count; char connect_address[sizeof("000.000.000.000")+1 ]; int mysql_version; }; </code></pre> <p>The method's signature is:</p> <pre><code> ndb_mgm_cluster_state* WINAPI wrap_ndb_mgm_get_status(HANDLE handle); </code></pre> <p>All of this is provided by a 3rd party library, so nothing can be changed. In C# i have the follow definitions:</p> <pre><code>[DllImport("Ndb_CWrapper.dll", CharSet = CharSet.Ansi)] private static extern IntPtr wrap_ndb_mgm_get_status(IntPtr handle); </code></pre> <p>the structures are:</p> <pre><code>[StructLayoutAttribute(LayoutKind.Sequential, CharSet = CharSet.Ansi)] public struct ndb_mgm_cluster_state { public int no_of_nodes; public IntPtr node_states; }; [StructLayoutAttribute(LayoutKind.Sequential, CharSet = CharSet.Ansi)] public struct ndb_mgm_node_state { public int node_id; public ndb_mgm_node_type node_type; public ndb_mgm_node_status node_status; public int start_phase; public int dynamic_id; public int node_group; public int version; public int connect_count; [MarshalAsAttribute(UnmanagedType.ByValTStr, SizeConst = 17)] public string connect_address; public int mysql_version; }; </code></pre> <p>I tried to unmarshal the results without success (i recieve an oddly error (not an Exception) Fatal error execution, can be a CLR bug or a miscall P/invoke.</p> <p>Obviously the reason is a problem in my P/Invoke call</p> <p>I tried in this way: First of all i unmarshalled the <code>ndb_mgm_cluster_state</code> structure:</p> <pre><code>var res=(ndb_mgm_cluster_state)Marshal.PtrToStructure( tmpPtr, typeof(ndb_mgm_cluster_state)); </code></pre> <p>where <code>IntPtr</code> is the result of the native call. Up to this step everything "seems" to be done right, but when i try to unmarshall the <code>node_states</code> i get the error:</p> <pre><code>ndb_mgm_node_state tmpNode = (ndb_mgm_node_state)Marshal.PtrToStructure( status.node_states, typeof(ndb_mgm_node_state)); </code></pre> <p>What can be the problem? I supposed is something related to the strange declaration of <code>ndb_mgm_cluster_state</code> because is defined an array of 1 element, but it contain several elements. (the number of elements is in <code>no_of_nodes</code>)</p> <p><strong>WORKAROUND:</strong></p> <p>The only way to let everything work i found is to change a bit the signature, in this way:</p> <pre><code>ndb_mgm_node_state* WINAPI wrap_ndb_mgm_get_status(HANDLE handle,int* length); </code></pre> <p>in C#:</p> <pre><code>[DllImport("Ndb_CWrapper.dll", CharSet = CharSet.Ansi)] private static extern IntPtr wrap_ndb_mgm_get_status(IntPtr handle,out int length); </code></pre> <p>where length contains <code>no_of_nodes</code></p> <p>the unmarshall will be in this way:</p> <pre><code>IntPtr tmpPtr = wrap_ndb_mgm_get_status(raw,out length); ndb_mgm_cluster_state tmpRes = new ndb_mgm_cluster_state(); tmpRes.no_of_nodes = length; tmpRes.node_states = new ndb_mgm_node_state[length]; int step=0; for (int i = 0; i &lt; tmpRes.no_of_nodes; i++) { tmpRes.node_states[i] = (ndb_mgm_node_state)Marshal.PtrToStructure( tmpPtr+(step*i), typeof(ndb_mgm_node_state)); step = Marshal.SizeOf(tmpRes.node_states[i]); } </code></pre> <p>I know the step calculation is odd at the monent, but its not that the point. there is no way to let the thing work returning directly the <code>ndb_mgm_cluster_state</code> struct instead of do all of this?</p>
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    1. PTQuestion
    1. USSalvatore Sorbello
    1. USSalvatore Sorbello
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    1. COIf this C# code `public IntPtr node_states;` declares as pointer, this does **not** match this member `struct ndb_mgm_node_state node_states[1];` on the C side, as the latter is an array with one element. There are no pointers here in C.
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      1. POUnmarshalling a Struct containing an array of structs
      1. USalk
    2. COThe code is compiled with a C++ compiler, when i declared the C# struct with public `ndb_mgm_node_state[1] nodestates` it does not work (even with all sort of MarshalAttribute option i can think of)
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      1. POUnmarshalling a Struct containing an array of structs
      1. USSalvatore Sorbello
 

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