Change all C code to return ndn_Error enum instead of char * error string.
diff --git a/ndn-cpp/c/encoding/BinaryXMLInterest.c b/ndn-cpp/c/encoding/BinaryXMLInterest.c
index a00d3be..1131428 100644
--- a/ndn-cpp/c/encoding/BinaryXMLInterest.c
+++ b/ndn-cpp/c/encoding/BinaryXMLInterest.c
@@ -8,9 +8,9 @@
 #include "BinaryXMLName.h"
 #include "BinaryXMLInterest.h"
 
-char *ndn_decodeBinaryXMLInterest(struct ndn_Interest *interest, struct ndn_BinaryXMLDecoder *decoder)
+ndn_Error ndn_decodeBinaryXMLInterest(struct ndn_Interest *interest, struct ndn_BinaryXMLDecoder *decoder)
 {
-  char *error;
+  ndn_Error error;
   if (error = ndn_BinaryXMLDecoder_readElementStartDTag(decoder, ndn_BinaryXML_DTag_Interest))
     return error;