Python: let lib.string() handle variable- and fixed-sized strings

src/main.cpp

@@ -589,7 +589,7 @@ int main(int argc, char **argv)
         size_t payload_size = jas_str.length() + bytecode.size() + 1;
         printf("\n%s dataset header:\n%s\n", info.name.c_str(), jas.dump(4).c_str());
         if (compound_declarations.size())
-            printf("\nCompound data structures available to the UDF:\n%s\n", compound_declarations.c_str());
+            printf("\nData structures available to the UDF:\n%s\n", compound_declarations.c_str());
 
         /* Sanity check: the JSON and the bytecode must fit in the dataset */
         hsize_t grid_size = std::accumulate(std::begin(info.dimensions), std::end(info.dimensions), 1, std::multiplies<hsize_t>());

src/udf_template.py

@@ -29,7 +29,11 @@ def load(self, filterpath):
     def string(self, structure):
         # Strings are embedded in a structure with a single
         # 'value' member.
-        return self.ffi.string(structure.value).decode("utf-8")
+        if hasattr(structure, "value"):
+            return self.ffi.string(structure.value).decode("utf-8")
+        # The user may also provide a direct pointer to the
+        # string member.
+        return self.ffi.string(structure).decode("utf-8")
 
     def getData(self, name):
         name = self.ffi.new("char[]", name.encode("utf-8"))

test/test-compound-string.py

@@ -0,0 +1,13 @@
+# hdf5-udf <file.h5> test-compound-string.py Temperature.py:1000:double
+def dynamic_dataset():
+    compound = lib.getData("Dataset1")
+    udf_data = lib.getData("Temperature.py")
+    udf_dims = lib.getDims("Temperature.py")
+
+    for i in range(udf_dims[0]):
+        print("serial: {}, location: {}, temperature: {:.6f}, pressure: {:.6f}".format(
+            compound[i].serial_number,
+            lib.string(compound[i].location),
+            compound[i].temperature,
+            compound[i].pressure), flush=True)
+        udf_data[i] = compound[i].temperature

test/test-string.cpp

@@ -6,9 +6,8 @@ extern "C" void dynamic_dataset()
     auto udf_data = lib.getData<double>("Temperature.cpp");
     auto udf_dims = lib.getDims("Temperature.cpp");
 
-    for (size_t i=0; i<input_dims[0]; ++i) {
+    for (size_t i=0; i<input_dims[0]; ++i)
         printf("%s\n", input_string[i].value);
-    }
 
     for (size_t i=0; i<udf_dims[0]; ++i)
         udf_data[i] = i * 1.0;