Pass String array as input into external C function - modelica

Question

I would like to pass a String vector into an external C function.
In a minimal example I just want to pass the String vectors (or 1D array) through the C function.
My Modelica function looks like:
function testreadstri
input String instri[2];
output String outstri[2];
external "C" test_stri(instri,, size(instri, 1), outstri);
annotation (Include="#include <ebcmysql.cpp>", Library="libmysql");
end testreadstri;
My C fucntion looks like:
void test_stri(const char* thestring, size_t nLines, const char **testresult)
{
//bout = 12.3;
size_t iLines;
//size_t nLines;
iLines = 0;
//nLines = 1;
while ( iLines <= nLines ) {
<LINE_OF_INTEREST>
iLines++;
}
}
I tried for <LINE_OF_INTEREST> the following lines:
testresult[iLines] = thestring[iLines];
strcpy(testresult[iLines], thestring[iLines]);
What works, but of course does not pass the input through as an output, is:
testresult[iLines] = "aTestString";
Is there any possibility to handle Modelica input String vectors in the external C function?
Thanks in advance!

Answer 1

Here's a short, self-contained and compilable example demonstrating both input string and output string handling of a pure external function in Modelica
model Model
function testreadstri
input String instri[2];
output String outstri[2];
external "C" test_stri(instri, size(instri, 1), outstri, size(outstri, 1));
annotation(Include="
#include \"ModelicaUtilities.h\"
#include <stdlib.h>
#include <string.h>
void test_stri(const char** thestring, size_t nLinesIn, const char** testresult, size_t nLinesOut)
{
size_t iLines;
// example for input string handling
for (iLines = 0; iLines < nLinesIn; iLines++) {
ModelicaFormatMessage(\"%s\\n\", thestring[iLines]);
}
// example for output string handling
for (iLines = 0; iLines < nLinesOut; iLines++) {
char* line = ModelicaAllocateStringWithErrorReturn(6);
if (line != NULL) {
strcpy(line, \"result\");
testresult[iLines] = line;
}
}
}");
end testreadstri;
String s[:] = testreadstri({"first", "second"});
end Model;

Answer 2

Yes, this is supported by the Modelica specification, see https://specification.modelica.org/v3.4/Ch12.html#argument-type-mapping.