Question

Calling C++ From C#

Asked by: srinivas_vemla

Calling C++ From C#

I have to use a C++ DLL (written by someone else) and call a method whose definition is:

unsigned long WINAPI GetSeed(const char *sT, const char *sD, const int& c);

I am trying to call it using the following code:

[DllImport(@"Rand.dll")]
private static extern ulong GetSeed(
[MarshalAs(UnmanagedType.BStr)] string sT,
[MarshalAs(UnmanagedType.BStr)] string sD,
[MarshalAs(UnmanagedType.LPArray)] Int32[] c);


int[] control = new int[1];
control[0] = 0;

ulong randomSeed = GetSeed("ALL", "39314", control);
MessageBox.Show("Returned: " + randomSeed.ToString());

This works but gives me a different result. I should obtain 193450366 but I always get 5325750857283046. Any idea if I am doing something wrong? I am refering the correct DLL.

Thanks

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Asked On
2007-11-09 at 12:42:38ID22951105
Tags

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call

Topic

C# Programming Language

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Answers

 

by: josgoodPosted on 2007-11-10 at 07:29:46ID: 20256012

I suggest typing GetSeed as Uint32.  Long in C++ is 32 bits, long in C# is 64 bits.

 

by: josgoodPosted on 2007-11-10 at 07:58:57ID: 20256100

I have just reproduced your problem (typing GetSeed as ulong in C#) and then corrected it by typing GetSeed as UInt32.

I should be more precise about the size of unsigned long in C++.  It is 32 bits in Microsoft's compilers, but that isn't guaranteed to be true for other compilers.  I can't find the standard's statement on this, but generally long is guaranteed to be at least as large as int.  So there's nothing that prevents a compiler from typing long as 64 bits, or any other size, as long as long is at least as large as int.

 

by: srinivas_vemlaPosted on 2007-11-11 at 08:10:23ID: 20259371

awesome josgood... that works... i had to finally change it to:

DllImport(@"Rand.dll")]
private static extern uint GetSeed(
[MarshalAs(UnmanagedType.LPArray)] byte[] sT,
[MarshalAs(UnmanagedType.LPArray)] byte[] sD,
[MarshalAs(UnmanagedType.LPArray)] Int32[] c);

and it works...

Thanks

20120131-EE-VQP-002

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