Question

I want to use LabVIEW’s Call Library Function Node to access a DLL function, and have this function return a string to displayed on my VI. How would I go about doing this? I am quite happy returning numbers from my DLL, but am really struggling to find any examples of how to return a string.

Answer 1

I assume from your question that you already have a DLL that can return numbers to Labview. To return a string from the DLL, I have created a DLL with the following C++ function

void returnString(char myString[]) {   const char *aString = 'test string';   memcpy(myString, aString, 12); } 

In Labview I then use the Call Library Function Node and configure it as follows

     Library Name or Path: c:\path\to\my\custom.dll            Function Name: returnString            Calling Convention: C      Parameters:             Parameter: return type                 type: void             Parameter: arg1                 type: String                 string format: C String Pointer      Function prototype:         void returnString(CStr arg1); 

After connect the arg1 output in the block diagram to a string indicator and run. The string ‘test string’ should appear in the front panel.

I tried to have the returnString function be of type CStr as in

CStr returnString() { ...  } 

but I got build errors when compiling the DLL project.

Update

Thanks to @bk1e comment don’t forget to pre-allocate space in Labview for the string.