Improve C standard compliance.

- Don't cast between object and function pointers.
- Use standard compliant `__VA_ARGS__` in macros.
- Add explicit `__extension__` on unnamed union in struct (it's a GNU
  extension).
- Remove ; after function definitions.
- Replace `const T foo = 3;` for integral types `T` with `enum { foo = 3 };`.
  Folding integral constants like that as compile time constants is a GNU
  extension. Arrays allocated with `foo` as dimension are VLAs on strictly
  compliant C99 compilers.
- Replace empty initialiser list `{}` with zero-initialiser-list `{0}`.
  The former is a GNU extension meaning the latter.
- Cast `T*` (where `T != void`) to `void *` in format arguments. While any
  object pointer can be implicitly converted to and from `void *`, this
  conversion does not happen in variadic function calls.
- Replace arithmetic on `void *` with arithmetic on `char *`. The former
  is non-compliant.
- Replace non-`int`-derived types (like `uint16_t`, which is
  `short`-derived) in bit fields with `int`-derived types. Using any type
  other than `int` or `unsigned int` (or any of their aliases) in bit
  fields is a GNU extension.

1 files changed, 2 insertions, 2 deletions

diff --git a/auto_tests/TCP_test.c b/auto_tests/TCP_test.c
index 8e6adf2e..d7312be8 100644
--- a/auto_tests/TCP_test.c
+++ b/auto_tests/TCP_test.c
@@ -310,7 +310,7 @@ static uint8_t response_callback_connection_id;
 static uint8_t response_callback_public_key[crypto_box_PUBLICKEYBYTES];
 static int response_callback(void *object, uint8_t connection_id, const uint8_t *public_key)
 {
-    if (set_tcp_connection_number(object - 2, connection_id, 7) != 0) {
+    if (set_tcp_connection_number((TCP_Client_Connection *)((char *)object - 2), connection_id, 7) != 0) {
         return 1;
     }
 
@@ -433,7 +433,7 @@ START_TEST(test_client)
     crypto_box_keypair(f2_public_key, f2_secret_key);
     ip_port_tcp_s.port = htons(ports[rand() % NUM_PORTS]);
     TCP_Client_Connection *conn2 = new_TCP_connection(ip_port_tcp_s, self_public_key, f2_public_key, f2_secret_key, 0);
-    routing_response_handler(conn, response_callback, ((void *)conn) + 2);
+    routing_response_handler(conn, response_callback, (char *)conn + 2);
     routing_status_handler(conn, status_callback, (void *)2);
     routing_data_handler(conn, data_callback, (void *)3);
     oob_data_handler(conn, oob_data_callback, (void *)4);