Should return std::string

This is only used in C++, so there is no need to g_strdup in here. Also,
this fixes a memory leak in KvpFrameImpl.

libgnucash/backend/xml/test/test-kvp-frames.cpp

@@ -35,7 +35,7 @@ test_kvp_get_slot (int run,
     {
         gchar* tmp;
         failure_args (msg, __FILE__, __LINE__, "run=%d", run);
-        printf ("    Value is %s\n", test_val2->to_string ());
+        printf ("    Value is %s\n", test_val2->to_string ().c_str ());
     }
 }
 

libgnucash/engine/kvp-value.cpp

@@ -149,16 +149,8 @@ struct to_string_visitor : boost::static_visitor<void>
         /*Since val is passed by value, we can modify it*/
         for (;val; val = val->next)
         {
-            gchar *tmp3;
             auto realvalue = static_cast<const KvpValue *>(val->data);
-            tmp3 = realvalue->to_string();
-            output << ' ';
-            if (tmp3)
-            {
-                output << tmp3;
-                g_free(tmp3);
-            }
-            output << ',';
+            output << ' ' << realvalue->to_string() << ',';
         }
 
         output << " ]";
@@ -207,7 +199,7 @@ struct to_string_visitor : boost::static_visitor<void>
     }
 };
 
-char *
+std::string
 KvpValueImpl::to_string() const noexcept
 {
     std::ostringstream ret;
@@ -215,7 +207,7 @@ KvpValueImpl::to_string() const noexcept
     boost::apply_visitor(visitor, datastore);
 
     /*We still use g_strdup since the return value will be freed by g_free*/
-    return g_strdup(ret.str().c_str());
+    return ret.str();
 }
 
 static int

libgnucash/engine/kvp-value.hpp

@@ -137,7 +137,7 @@ struct KvpValueImpl
 
     KvpValueImpl::Type get_type() const noexcept;
 
-    char * to_string() const noexcept;
+    std::string to_string() const noexcept;
 
     template <typename T>
     T get() const noexcept;