pass char array to c++ DLL and return same char array

[Jeroen_Mechatronics]

Lectori Salutem,

Here is the situation:

Im learning TestStand, and to learn the basics, I want to do the following:

Call a (C++) DLL in TestStand with an array of chars.

The DLL should return the array of chars (or a pointer to the datalocation).

This is the code in my DLL:

//////////////////////////////////////////////////////////////////////////////

TESTDLL3_API char* bounceString(char data[])

{

  data = "Hello World";

  cout << data;

char* pointer = data;

return pointer;

}

//////////////////////////////////////////////////////////////////////////////

However, this function will not be recognized by TestStand 😞

When this is working, I think I can build the rest of the functionality by myself.

Thanks in advance for any help!

Jeroen

The Netherlands

[j_dodek]

Hi Jeroen,

Have you ever looked in TS-Example foulder: Examples\AccessingPropertiesUsingAPI\UsingMFC

In this Example there is a hole Visual Studio Project. Maybe you can use this for starting on scratch.

For passing strings back to TS, you should take a look on the CVI c-code Example in

Examples\Demo\C\Auto.c "Ignition_Test(xxx)"

Hope this helps

Juergen

[Jeroen_Mechatronics]

Sadly, in the example there is no return value to TestStand.

However, I did manage to return the pointer of the char array to TestStand:

/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

int __declspec( dllexport )  bounceString2(char* argument)

{

  void *pointer;

  int i;

  argument = "Hello";

  pointer = argument;

  i = (int) pointer;

  return i;

}

/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

So, right now I have to find out how to retrieve the char array from the pointer...

Jeroen

PS, I will look at the CVI code, and let you know about my process

[Jeroen_Mechatronics · Accepted solution]

Fixed it 😄

It turns out, I had to declare a string variable in TestStand.

TestStand:

declare Locals.Text (string)

call the DLL module, with arg1 = char[1024] = Locals.Text

After calling the DLL, Locals.Text becomes Hello :D:D

Visual Studio DLL code:

void __declspec( dllexport )  bounceString2(char argument[])

{

  strcpy(argument, "Hello");

}

Anyone, thanks for the help!

Jeroen

[Josh_W]

Just to expand on this for anyone who finds this post later.

TestStand doesn't support functions that return char* because it can't deallocate the memory. So if you need a string back, it has to be passed as a parameter.

See this post by a TestStand devloper for more info:

http://forums.ni.com/t5/NI-TestStand/TestStand-pointeur-en-valeur-retourn%C3%A9e/m-p/904912/message-...