Fix dereference of expired temporaries.

Reported by clang 15.0.7, which will be in Ubuntu 23.04, -Wdangling-gsl

libgnucash/backend/xml/test/test-file-stuff.cpp

@@ -261,13 +261,10 @@ equals_node_val_vs_kvp_frame (xmlNodePtr node, const KvpFrame* frm)
     }
     else
     {
-        auto frm1str = g_strdup (frm->to_string ().c_str ());
-        auto frm2str = g_strdup (cmpfrm->to_string ().c_str ());
+        auto frmstr = frm->to_string ();
+        auto cmpfrmstr = cmpfrm->to_string ();
 
-        printf ("%s vs %s\n", frm1str, frm2str);
-
-        g_free (frm1str);
-        g_free (frm2str);
+        printf ("%s vs %s\n", frmstr.c_str(), cmpfrmstr.c_str());
 
         delete cmpfrm;
         return FALSE;

libgnucash/core-utils/gnc-filepath-utils.cpp

@@ -211,7 +211,10 @@ gchar *gnc_file_path_relative_part (const gchar *prefix, const gchar *path)
 {
     std::string p{path};
     if (p.find(prefix) == 0)
-        return g_strdup(p.substr(strlen(prefix)).c_str());
+    {
+        auto str = p.substr(strlen(prefix));
+        return g_strdup(str.c_str());
+    }
     return g_strdup(path);
 }
 

libgnucash/engine/gnc-date.cpp

@@ -1101,7 +1101,8 @@ qof_strftime(gchar *buf, gsize max, const gchar *format, const struct tm *tm)
 gchar *
 gnc_date_timestamp (void)
 {
-    return g_strdup(GncDateTime::timestamp().c_str());
+    auto timestamp = GncDateTime::timestamp();
+    return g_strdup(timestamp.c_str());
 }
 
 /********************************************************************\

libgnucash/engine/gnc-features.cpp

@@ -65,10 +65,13 @@ header = N_("This Dataset contains features not supported "
 gchar *gnc_features_test_unknown (QofBook *book)
 {
     auto unknowns {qof_book_get_unknown_features (book, features_table)};
+    if (unknowns.empty())
+        return nullptr;
+
     auto accum = [](const auto& a, const auto& b){ return a + "\n* " + b; };
-    return unknowns.empty() ? nullptr :
-        g_strdup (std::accumulate (unknowns.begin(), unknowns.end(),
-                                   std::string (_(header)), accum).c_str());
+    auto msg {std::accumulate (unknowns.begin(), unknowns.end(),
+                                   std::string (_(header)), accum)};
+    return g_strdup (msg.c_str());
 }
 
 void gnc_features_set_used (QofBook *book, const gchar *feature)

libgnucash/engine/gnc-optiondb.cpp

@@ -459,7 +459,10 @@ GncOptionDB::save_to_kvp(QofBook* book, bool clear_options) const noexcept
                              * have to store. */
                             kvp = new KvpValue(option.template get_value<double>());
                         else
-                            kvp = new KvpValue{g_strdup(option.template get_value<std::string>().c_str())};
+                        {
+                            auto str{option.template get_value<std::string>()};
+                            kvp = new KvpValue{g_strdup(str.c_str())};
+                        }
                         qof_book_set_option(book, kvp, &list_head);
                     }
                 });

libgnucash/engine/qofinstance.cpp

@@ -1102,8 +1102,8 @@ qof_instance_compare_kvp (const QofInstance *a, const QofInstance *b)
 char*
 qof_instance_kvp_as_string (const QofInstance *inst)
 {
-    //The std::string is a local temporary and doesn't survive this function.
-    return g_strdup(inst->kvp_data->to_string().c_str());
+    auto str{inst->kvp_data->to_string()};
+    return g_strdup(str.c_str());
 }
 
 void