Add function to allow getting string-valued auth_asym_id/chain-labels…

… from atoms.

Related to #96.

src/freesasa.h

@@ -1130,6 +1130,22 @@ freesasa_structure_atom_res_number(const freesasa_structure *structure,
 char freesasa_structure_atom_chain(const freesasa_structure *structure,
                                    int i);
 
+/**
+    \private
+    Get long form chain label.
+
+    Asserts that index i is within bounds.
+
+    @param structure The structure.
+    @param i Atom index.
+    @return Chain label (`'A'`, `'B'`, etc.)
+
+    @ingroup structure
+ */
+const char *
+freesasa_structure_atom_chain_lcl(const freesasa_structure *structure,
+                                  int i);
+
 /**
     Get atom symbol.
 

src/structure.c

@@ -1068,6 +1068,16 @@ char freesasa_structure_atom_chain(const freesasa_structure *structure,
     assert(i < structure->atoms.n && i >= 0);
     return structure->atoms.atom[i]->chain_label[0];
 }
+
+const char *
+freesasa_structure_atom_chain_lcl(const freesasa_structure *structure,
+                                  int i)
+{
+    assert(structure);
+    assert(i < structure->atoms.n && i >= 0);
+    return structure->atoms.atom[i]->chain_label;
+}
+
 const char *
 freesasa_structure_atom_symbol(const freesasa_structure *structure,
                                int i)

tests/test_structure.c

@@ -146,6 +146,7 @@ START_TEST(test_cif)
         ck_assert_str_eq(freesasa_structure_atom_res_number(s, i), rnu[i]);
         ck_assert_str_eq(freesasa_structure_atom_symbol(s, i), symbol[i]);
         ck_assert_int_eq(freesasa_structure_atom_chain(s, i), lcl[i][0]);
+        ck_assert_str_eq(freesasa_structure_atom_chain_lcl(s, i), lcl[i]);
     }
 
     struct freesasa_cif_atom_lcl atom = {