As an alternative, you can append all diagnostic messages into one string and just return a list of the diagnostic string and the result list.

In this approach, you would do a sequence of sprintf() calls.

sprintf(Buffer,"diag1\n");
sprintf(Buffer + strlen(Buffer),"diag2\n");

or track and use the length returned by sprintf().

Regards,

Neil

Brian,

I would combine all the strings into a list and return them to Mathematica along with your result. The result would be in this form: List[List[diag1,diag2,...], List[Real1,Real2,Real3,...]]

WSPutFunction(stdlink, "List", 2);
WSPutFunction(stdlink, "List", 43);
WSPutString(stdlink,diagtxt1);
...
WSPutString(stdlink,diagtxt43);
WSPutReal64List(stdlink, result, size);

You can read about it in this tutorial. Search for

You can use WSTP functions to create absolutely any Wolfram Language expression. The basic idea is to call a sequence of WSTP functions that correspond directly to the FullForm representation of the Wolfram Language expression.

Regards,

Neil