Add API documentation

Author: gassmoeller

doc/sphinx/api_manual/API_FFI/C_interface.md

@@ -4,4 +4,4 @@ C interface
 
 ```{todo}
 Explain how to use the C interface in your program. Point to or show the example in the example directory.
-```
+```

doc/sphinx/index.md

@@ -53,6 +53,7 @@ developer_manual/start_devel_and_contrib/index
 developer_manual/contributing_to_the_documentation/index
 developer_manual/contributing_to_the_code/index
 developer_manual/developing_for_the_GWB/index
+Source code documentation <https://codedocs.xyz/GeodynamicWorldBuilder/WorldBuilder/index.html>
 
 ```
 

include/world_builder/wrapper_c.h

@@ -22,6 +22,16 @@
 
 #include <stdbool.h>
 
+/** @file
+ * This file contains the C API of the WorldBuilder library.
+ *
+ * The C API is used to make the WorldBuilder library available to programs written
+ * in C. The C API is a set of functions that can be called from C code. The
+ * functions in the C API call the corresponding C++ functions in the WorldBuilder
+ * library. Check the content of this file for a list of the available functions and
+ * their documentation.
+ */
+
 #ifdef __cplusplus
 extern "C" {
 #endif

include/world_builder/wrapper_cpp.h

@@ -23,6 +23,9 @@
 #include <string>
 #include "world_builder/deprecate.h"
 
+/**
+ * This namespace contains the C++ wrapper of the WorldBuilder library.
+ */
 namespace wrapper_cpp
 {
   /**

source/world_builder/wrapper_fortran.f90

@@ -17,6 +17,12 @@
 !!  along with this program.  If not, see <https://www.gnu.org/licenses/>.
 !!
 
+!> This module contains the Fortran API of the World Builder library.
+!! The Fortran API is used to make the WorldBuilder library available to programs written
+!! in Fortran. The Fortran API is a set of functions that can be called from C code. The
+!! functions in the C API call the corresponding C++ functions in the WorldBuilder
+!! library. Check the content of this module for a list of the available functions and
+!! their documentation.
 MODULE WorldBuilder
 USE, INTRINSIC :: ISO_C_BINDING!, ONLY: C_PTR
   IMPLICIT NONE