send.h: Document cpp magic.

These macros are not completely trivial, so give the interested reader
an idea about how the macros help to avoid code duplication.

diff --git a/send.h b/send.h
index 67b47e48d9e7fd0b96fa4c5c7abd95594c6e2cf0..8f7005cdaa78f0909808932e602fc7de7945dd52 100644 (file)
--- a/send.h
+++ b/send.h
@@ -2,6 +2,10 @@
 
 /** \file send.h Sender-related defines and structures. */
 
+/**
+ * A little preprocessor fu helps to create the sender_subcommand enumeration
+ * below and the list of sender name strings without duplicating the commands.
+ */
 #define SENDER_SUBCOMMANDS \
        SENDER_SUBCOMMAND(add) /**< Add a target (udp only). */ \
        SENDER_SUBCOMMAND(delete) /**< Delete a target (udp only). */ \
@@ -10,12 +14,27 @@
        SENDER_SUBCOMMAND(on) /**< Activate the sender. */ \
        SENDER_SUBCOMMAND(off) /**< Deactivate the sender. */ \
 
+/** Concatenate "SENDER_" and the given arg and append a comma. */
 #define SENDER_SUBCOMMAND(_name) SENDER_ ## _name,
+
+/**
+ * Each sender subcommand gets an SENDER_xxx identifier. The identifier is
+ * passed from the sender command handler to the server process via shared
+ * memory.
+ */
 enum sender_subcommand {
-       SENDER_SUBCOMMANDS
+       SENDER_SUBCOMMANDS /**< List of SENDER_xxx identifiers. */
        NUM_SENDER_CMDS /**< Used as array size in struct \ref sender. */
 };
+
 #undef SENDER_SUBCOMMAND
+
+/**
+ * Redefine it to expand to the stringified name of the sender so that
+ * SENDER_SUBCOMMANDS above now expands to the comma-separated list of sender
+ * name strings. This is used in command.c to define and initialize an array of
+ * char pointers.
+ */
 #define SENDER_SUBCOMMAND(_name) #_name,
 
 /**