Update json_util

filename should be passed as const char* to functions
json_object_to_file and json_object_to_file

json_util.c

@@ -99,7 +99,7 @@ struct json_object* json_object_from_file(const char *filename)
 
 /* extended "format and write to file" function */
 
-int json_object_to_file_ext(char *filename, struct json_object *obj, int flags)
+int json_object_to_file_ext(const char *filename, struct json_object *obj, int flags)
 {
   const char *json_str;
   int fd, ret;
@@ -141,7 +141,7 @@ int json_object_to_file_ext(char *filename, struct json_object *obj, int flags)
 
 // backwards compatible "format and write to file" function
 
-int json_object_to_file(char *filename, struct json_object *obj)
+int json_object_to_file(const char *filename, struct json_object *obj)
 {
   return json_object_to_file_ext(filename, obj, JSON_C_TO_STRING_PLAIN);
 }

json_util.h

@@ -22,8 +22,8 @@ extern "C" {
 
 /* utility functions */
 extern struct json_object* json_object_from_file(const char *filename);
-extern int json_object_to_file(char *filename, struct json_object *obj);
-extern int json_object_to_file_ext(char *filename, struct json_object *obj, int flags);
+extern int json_object_to_file(const char *filename, struct json_object *obj);
+extern int json_object_to_file_ext(const char *filename, struct json_object *obj, int flags);
 extern int json_parse_int64(const char *buf, int64_t *retval);
 extern int json_parse_double(const char *buf, double *retval);