qstring: Make conversion from QObject * accept null

qobject_to_qstring() crashes on null, which is a trap for the unwary.
Return null instead, and simplify a few callers.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <1444918537-18107-7-git-send-email-armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Luiz Capitulino <lcapitulino@redhat.com>

2 files changed, 5 insertions, 10 deletions

diff --git a/qobject/qdict.c b/qobject/qdict.c
index 97e881b3a4..2d67bf1579 100644
--- a/qobject/qdict.c
+++ b/qobject/qdict.c
@@ -282,8 +282,7 @@ QDict *qdict_get_qdict(const QDict *qdict, const char *key)
  */
 const char *qdict_get_str(const QDict *qdict, const char *key)
 {
-    QObject *obj = qdict_get_obj(qdict, key, QTYPE_QSTRING);
-    return qstring_get_str(qobject_to_qstring(obj));
+    return qstring_get_str(qobject_to_qstring(qdict_get(qdict, key)));
 }
 
 /**
@@ -325,13 +324,9 @@ bool qdict_get_try_bool(const QDict *qdict, const char *key, bool def_value)
  */
 const char *qdict_get_try_str(const QDict *qdict, const char *key)
 {
-    QObject *obj;
-
-    obj = qdict_get(qdict, key);
-    if (!obj || qobject_type(obj) != QTYPE_QSTRING)
-        return NULL;
+    QString *qstr = qobject_to_qstring(qdict_get(qdict, key));
 
-    return qstring_get_str(qobject_to_qstring(obj));
+    return qstr ? qstring_get_str(qstr) : NULL;
 }
 
 /**
diff --git a/qobject/qstring.c b/qobject/qstring.c
index 607b7a142c..cb72dfbfc8 100644
--- a/qobject/qstring.c
+++ b/qobject/qstring.c
@@ -117,9 +117,9 @@ void qstring_append_chr(QString *qstring, int c)
  */
 QString *qobject_to_qstring(const QObject *obj)
 {
-    if (qobject_type(obj) != QTYPE_QSTRING)
+    if (!obj || qobject_type(obj) != QTYPE_QSTRING) {
         return NULL;
-
+    }
     return container_of(obj, QString, base);
 }