19.2.3 Using a library

Once again, the project facility greatly simplifies the use of libraries. In this context, using a library is just a matter of adding a with clause in the user project. For instance, to make use of the library My_Lib shown in examples in earlier sections, you can write:

     with "my_lib";
     project My_Proj is
       ...
     end My_Proj;

Even if you have a third-party, non-Ada library, you can still use GNAT's Project Manager facility to provide a wrapper for it. For example, the following project, when withed by your main project, will link with the third-party library liba.a:

     project Liba is
        for Source_Dirs use ();
        for Library_Dir use "lib";
        for Library_Name use "a";
        for Library_Kind use "static";
     end Liba;

In order to use an Ada library manually, you need to make sure that this library is on both your source and object path (see Search Paths and the Run-Time Library (RTL) and Search Paths for gnatbind). Furthermore, when the objects are grouped in an archive or a shared library, you need to specify the desired library at link time.

For example, you can use the library mylib installed in /dir/my_lib_src and /dir/my_lib_obj with the following commands:

     $ gnatmake -aI/dir/my_lib_src -aO/dir/my_lib_obj my_appl \
       -largs -lmy_lib

This can be expressed more simply:

     $ gnatmake my_appl

when the following conditions are met:

• /dir/my_lib_src has been added by the user to the environment variable ADA_INCLUDE_PATH, or by the administrator to the file ada_source_path
• /dir/my_lib_obj has been added by the user to the environment variable ADA_OBJECTS_PATH, or by the administrator to the file ada_object_path
• a pragma Linker_Options has been added to one of the sources. For example:

            pragma Linker_Options ("-lmy_lib");