<para><function>sd_bus_message_is_signal()</function> checks if message <parameter>m</parameter>
is a signal message. If <parameter>interface</parameter> is non-null, it also checks if the
message has the same interface set. If <parameter>member</parameter> is non-null, it also checks
if the message has the same member set. Also see
<citerefentry><refentrytitle>sd_bus_set_message_new_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>. It returns true when all checks pass.</para>
<para><function>sd_bus_message_is_method_call()</function> checks if message <parameter>m</parameter>
is a method call message. If <parameter>interface</parameter> is non-null, it also checks if the
message has the same interface set. If <parameter>member</parameter> is non-null, it also checks
if the message has the same member set. Also see
<citerefentry><refentrytitle>sd_bus_set_message_new_method_call</refentrytitle><manvolnum>3</manvolnum></citerefentry>. It returns true when all checks pass.</para>
<para><function>sd_bus_message_is_method_error()</function> checks if message <parameter>m</parameter>
is an error reply message. If <parameter>name</parameter> is non-null, it also checks if the
message has the same error identifier set. Also see
<citerefentry><refentrytitle>sd_bus_set_message_new_method_error</refentrytitle><manvolnum>3</manvolnum></citerefentry>. It returns true when all checks pass.</para>
</refsect1>
<refsect1>
<title>Return Value</title>
<para>On success, those functions return 0 or a positive
integer. On failure, it returns a negative errno-style error code.</para>