- \ref GRAS_tut_tour_globals_use
- \ref GRAS_tut_tour_callback_pitfall
- \ref GRAS_tut_tour_callback_recap
-
+
<hr>
\section GRAS_tut_tour_globals_intro Introduction
the several instances of your process, leading to bad problems.
Instead, you you have to put all globals in a structure, and let GRAS handle
-it with the gras_userdata_* functions (there is only 3 of them ;).
+it with the gras_userdata_* functions (there is only 3 of them ;).
\section GRAS_tut_tour_globals_use Putting globals into action
We will now modify the example to add a "kill" message, and let the server
loop on incoming messages until it gets such a message. We only need a
-boolean, so the structure is quite simple:
+boolean, so the structure is quite simple:
\dontinclude 05-globals.c
\skip struct
\until server_data
-
+
Then, we need to create this structure in the process main function. We
could use either gras_userdata_new() or gras_userdata_set(). The former is an
helper macro mallocing the space needed by the structure and passing it to
\skip userdata_new
\until userdata_new
+BEWARE, the gras_userdata_new expects the pointed type, not the
+pointer type. As you can see, in our example, you should pass
+server_data_t to the macro, even if the global variable is later
+defined as being of type server_data_t*.
+
Once you declared a global that way, retriving this (for example in a
callback) is really easy:
\dontinclude 05-globals.c
\skip while
\until }
+Please note that in our example, only one process creates a global
+structure. But this is naturally completely ok to have several
+processes creating their globals this way. Each of these globals will
+be separated, so process A cannot access globals defined by process B.
+Maybe this implies that the name "globals" is a bit misleading. It
+should be "process state" or something similar.
+
\section GRAS_tut_tour_callback_pitfall Common pitfall of globals
There is an error that I do myself every other day using globals in GRAS.
\verbatim int server(int argc, char *argv[]) {
server_data_t globals=gras_user_new(server_data_t);
/* other variable definition */
-
+
gras_init(&argc, argv);
-
+
/* rest of the code */
}\endverbatim
and cannot store your data anywhere. That is why doing so triggers an error
at run time.
+Also, as noted above, the gras_userdata_new expects the pointed type,
+not the pointer type. As you can see, in our example, you should pass
+server_data_t to the macro, even if the global variable is later
+defined as being of type server_data_t*.
+
+
\section GRAS_tut_tour_callback_recap Recaping everything together
The whole program now reads:
