qobject: introduce qobject_get_try_str()

A quick way to fetch string from qobject when it's a QString.

Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20180309090006.10018-4-peterx@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
[eblake: rebase to qobject_to() macro]
Signed-off-by: Eric Blake <eblake@redhat.com>

diff --git a/include/qapi/qmp/qstring.h b/include/qapi/qmp/qstring.h
index 38c680b7185847c824b5e213f978b82c9b3da113..30ae260a7fc3e43034ce6d5459b504411cbfde20 100644 (file)
--- a/include/qapi/qmp/qstring.h
+++ b/include/qapi/qmp/qstring.h
@@ -28,6 +28,7 @@ QString *qstring_from_substr(const char *str, int start, int end);
 size_t qstring_get_length(const QString *qstring);
 const char *qstring_get_str(const QString *qstring);
 const char *qstring_get_try_str(const QString *qstring);
+const char *qobject_get_try_str(const QObject *qstring);
 void qstring_append_int(QString *qstring, int64_t value);
 void qstring_append(QString *qstring, const char *str);
 void qstring_append_chr(QString *qstring, int c);

diff --git a/qobject/qstring.c b/qobject/qstring.c
index 5777f0af231570f6231dce6dadacd20c9c9440aa..afca54b47ae30e73043344e90987f1d20cc31aa4 100644 (file)
--- a/qobject/qstring.c
+++ b/qobject/qstring.c
@@ -126,6 +126,17 @@ const char *qstring_get_try_str(const QString *qstring)
     return qstring ? qstring_get_str(qstring) : NULL;
 }
 
+/**
+ * qobject_get_try_str(): Return a pointer to the corresponding string
+ *
+ * NOTE: the string will only be returned if the object is valid, and
+ * its type is QString, otherwise NULL is returned.
+ */
+const char *qobject_get_try_str(const QObject *qstring)
+{
+    return qstring_get_try_str(qobject_to(QString, qstring));
+}
+
 /**
  * qstring_is_equal(): Test whether the two QStrings are equal
  */