Added tng_molecule_of_index_get()

2 files changed, 34 insertions, 0 deletions

diff --git a/include/tng_io.h b/include/tng_io.h
index 1a584e3..6ce98d0 100644
--- a/include/tng_io.h
+++ b/include/tng_io.h
@@ -1477,6 +1477,22 @@ tng_function_status DECLSPECDLLEXPORT tng_molecule_find
                  tng_molecule_t *molecule);
 
 /**
+ * @brief Retrieve the molecule with specified index in the list of molecules.
+ * @param tng_data is the trajectory data container containing the molecule.
+ * @param index is the index (in tng_data->molecules) of the molecule to return
+ * @param molecule is a pointer to the molecule if it was found - otherwise 0.
+ * @pre \code tng_data != 0 \endcode The trajectory container (tng_data)
+ * must be initialised before using it.
+ * @pre \code molecule != 0 \endcode molecule must not be a NULL pointer.
+ * @return TNG_SUCCESS (0) if the molecule is found or TNG_FAILURE (1) if the
+ * molecule is not found.
+ */
+tng_function_status DECLSPECDLLEXPORT tng_molecule_of_index_get
+                (tng_trajectory_t tng_data,
+                 int64_t index,
+                 tng_molecule_t *molecule);
+
+/**
  * @brief Find a chain in a molecule.
  * @param tng_data is the trajectory data container containing the molecule.
  * @param molecule is the molecule in which to search for the chain.
diff --git a/src/lib/tng_io.c b/src/lib/tng_io.c
index 1fcc7d9..364df13 100644
--- a/src/lib/tng_io.c
+++ b/src/lib/tng_io.c
@@ -7164,6 +7164,7 @@ tng_function_status DECLSPECDLLEXPORT tng_molecule_find
 
     TNG_ASSERT(tng_data, "TNG library: Trajectory container not properly setup.");
     TNG_ASSERT(name, "TNG library: name must not be a NULL pointer.");
+    TNG_ASSERT(molecule, "TNG library: molecule must not be a NULL pointer.");
 
     n_molecules = tng_data->n_molecules;
 
@@ -7184,6 +7185,23 @@ tng_function_status DECLSPECDLLEXPORT tng_molecule_find
     return(TNG_FAILURE);
 }
 
+tng_function_status DECLSPECDLLEXPORT tng_molecule_of_index_get
+                (tng_trajectory_t tng_data,
+                 int64_t index,
+                 tng_molecule_t *molecule)
+{
+    TNG_ASSERT(tng_data, "TNG library: Trajectory container not properly setup.");
+    TNG_ASSERT(molecule, "TNG library: molecule must not be a NULL pointer.");
+
+    if(index >= tng_data->n_molecules)
+    {
+        *molecule = 0;
+        return(TNG_FAILURE);
+    }
+    *molecule = &tng_data->molecules[index];
+    return(TNG_SUCCESS);
+}
+
 tng_function_status DECLSPECDLLEXPORT tng_molecule_chain_find
                 (tng_trajectory_t tng_data,
                  tng_molecule_t molecule,