Managed C++ & P/Invoke in a web serice

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MarkOwen - 16 Jun 2005 20:19 GMT

I am exploring using P/Invoke to call some legacy code from our customer
contact software. I have been trying some simple test scenarios and haven't
had success. Can someone point me to an example that shows how this can be
done? Here is a snippet of code I am trying:

Header file of C++ class for web service:

[DllImport("kernel32.dll", SetLastError=true)]
extern "C" bool GetComputerName(String *name, int *len);

Class file for web service:

String __gc* callKAPIClass::HelloWorld()
{
    String *p = "1234567890123456789012345678901234567890";
    int len = 30;
    bool rc = true;

    rc = GetComputerName(p, &len);
    int rc2 = Marshal::GetLastWin32Error();

    return p;
}

Unfortunately, I always get an error in GetComputerName().

Mark

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Carl Daniel [VC++ MVP] - 16 Jun 2005 20:31 GMT

> I am exploring using P/Invoke to call some legacy code from our
> customer contact software. I have been trying some simple test
[quoted text clipped - 22 lines]
>
> Unfortunately, I always get an error in GetComputerName().

Not surprising, since GetComputerName doesn't have any idea what to do with
a String*.

My suggestion would be to not use PInvoke. Rather, just call the function
from your C++ code and rely on IJW to bridge the managed/unmanaged gap.

<untested code>
#include <windows.h>

String __gc* callKAPIClass::HelloWorld()
{
char sz[MAX_COMPUTERNAME_LENGTH + 1];
int len = sizeof(sz);
bool rc = true;

rc = GetComputerName(sz, &len);
int rc2 = Marshal::GetLastWin32Error();

return Marshal.PtrToStringAuto(static_cast<IntPtr>(sz),len);
}
</untested code>

-cd

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Managed C++ & P/Invoke in a web serice

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