diff options
| author | Ran Benita <ran234@gmail.com> | 2014-01-18 17:10:53 +0200 |
|---|---|---|
| committer | Uli Schlachter <psychon@znc.in> | 2014-02-19 22:01:58 +0100 |
| commit | 4ffa6f83b92763eb901c7ddb7c20775e24d507ca (patch) | |
| tree | c94482763a0c3785fa196a4acf89f1bbbeb3a8c4 | |
| parent | d7eb0bdf3b5b11ee9f40ee5e73df8fc0bdfa59f3 (diff) | |
Add comments about how _xcb_conn_ret_error() works
If xcb_connect() fails, it doesn't return NULL. Instead, it always
returns an xcb_connection_t*, and the user should check for errors with
the xcb_connection_has_error() function. What this function does is
check if conn->has_error contains a non-zero error code, and returns it.
If an error did occur, xcb doesn't actually return a full
xcb_connection_t though, it just returns (xcb_connection_t *)
error_code. Since the 'has_error' field is the first, it is still
possible to check conn->has_error.
That last trick was not immediately obvious to me, so add some guiding
comments. This also ensures no one obliviously rearranges the struct.
Signed-off-by: Ran Benita <ran234@gmail.com>
Signed-off-by: Uli Schlachter <psychon@znc.in>
| -rw-r--r-- | src/xcb_conn.c | 3 | ||||
| -rw-r--r-- | src/xcbint.h | 1 |
2 files changed, 4 insertions, 0 deletions
diff --git a/src/xcb_conn.c b/src/xcb_conn.c index 46390e1..00c458f 100644 --- a/src/xcb_conn.c +++ b/src/xcb_conn.c @@ -374,6 +374,9 @@ void _xcb_conn_shutdown(xcb_connection_t *c, int err) /* Return connection error state. * To make thread-safe, I need a seperate static * variable for every possible error. + * has_error is the first field in xcb_connection_t, so just + * return a casted int here; checking has_error (and only + * has_error) will be safe. */ xcb_connection_t *_xcb_conn_ret_error(int err) { diff --git a/src/xcbint.h b/src/xcbint.h index b25f03b..67cf571 100644 --- a/src/xcbint.h +++ b/src/xcbint.h @@ -192,6 +192,7 @@ void _xcb_ext_destroy(xcb_connection_t *c); /* xcb_conn.c */ struct xcb_connection_t { + /* This must be the first field; see _xcb_conn_ret_error(). */ int has_error; /* constant data */ |