From 2ce552b5f783b6c761f473990df9ce93ef03dcf0 Mon Sep 17 00:00:00 2001 From: Carl Worth Date: Wed, 21 Oct 2009 23:01:17 -0700 Subject: [PATCH] Fix lifetime-maintenance bug with std::string and c_str() Here's more evidence that C++ is a nightmare to program---or that I'm smart enough to realize that C++ is more clever than I will ever be. Most of my issues with C++ have to do with it hiding things from me that I'd really like to and expect to be aware of as a C programmer. For example, the specific problem here is that there's a short-lived std::string, from which I just want to copy the C string. I try to do that on the next line, but before I can, C++ has already called the destructor on the std::string. Now, C++ isn't alone in doing garbage collecting like this. But in a *real* garbage-collecting system, everything would work that way. For example, here, I'm still holding a pointer to the C string contents, so if the garbage collector were aware of that reference, then it might clean up the std::string container and leave the data I'm still using. But that's not what we get with C++. Instead, some things are reference counted and collected, (like the std::string), and some things just aren't (like the C string it contains). The end result is that it's very fragile. It forces me to be aware of the timing of hidden functions. In a "real" system I wouldn't have to be aware of that timing, and in C the function just wouldn't be hidden. --- message.cc | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/message.cc b/message.cc index 8ca8fdee..24dbae91 100644 --- a/message.cc +++ b/message.cc @@ -176,14 +176,14 @@ notmuch_thread_ids_t * notmuch_message_get_thread_ids (notmuch_message_t *message) { notmuch_thread_ids_t *thread_ids; - const char *id_str; + std::string id_str; thread_ids = talloc (message, notmuch_thread_ids_t); if (unlikely (thread_ids == NULL)) return NULL; - id_str = message->doc.get_value (NOTMUCH_VALUE_THREAD).c_str (); - thread_ids->next = talloc_strdup (message, id_str); + id_str = message->doc.get_value (NOTMUCH_VALUE_THREAD); + thread_ids->next = talloc_strdup (message, id_str.c_str ()); /* Initialize thread_ids->current and terminate first ID. */ notmuch_thread_ids_advance (thread_ids); -- 2.43.0