LabVIEW
Problem in calling LabVIEW DLL with C#
Solved!
You need to preallocate output arrays and strings!
private void button1_Click(object sender, EventArgs e)
{
string output;
int[] value;
StringOutput("A", "B", out output, 3, out value, 4);
}
}
Your output and value variable need to be preallocated to provide storage for 3 resp. 4 elements. And since you want to receive a NULL terminated C string you need to increase this to 4 characters.
Also string in C# is an object not a C string pointer. You need to declare the StringOutput() function as follows:
[DllImport("SharedLib.dll",CallingConvention=CallingConvention.StdCall, Charset=CharSet.Ansi]
internal static extern int StringOutput(StringBuilder A, StringBuilder B, out StringBuilder StringOutput, int sizeString, out int[] output, int sizeArray);
Then call it similar to this:
StringBuilder output = new StringBuilder(4);
int[4] array = new int[4];
StringOutput("A", "B", output, output.Capacity, value, value.Length);Please note, I'm not a pro in C# and usually don't do much in it. Also this code has not been tested nor compiled at all, so likely contains some errors. It does however point you in the direction of where to look further.
What you need to understand is that the C DLL that you have created in LabVIEW has a so called unmanaged interface. This means C# is not able to know how to manage memory for the parameters at all and you have to do everything yourself, hence the requirement to explicitedly initialize the output and array variables with a preallocated memory block.
First, you should not hijack this thread for your highly unrelated problem.
Second, Callback functions are not something you can do natively with the Call Library Node. The most easiest solution is to write an external shared library in C that wraps your API function and provides the necessary callback function. This callback function then translates the even into a user event or occurrence which are the LabVIEW equivalents for callback functions. Look for PostLVUserEvent() here on the NI site or over on www.lavag.org to find several discussions about how to use user events to receive the callback events.
