Re: [PATCH] don't store temporary value returned from c_str()

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+Date: Wed, 1 May 2013 13:28:06 +0200\r
+From: Vladimir Marek <Vladimir.Marek@Oracle.COM>\r
+To: Kim Minh Kaplan <kimminh.kaplan+nomuch@afnic.fr>\r
+Subject: Re: [PATCH] don't store temporary value returned from c_str()\r
+Message-ID: <20130501112806.GD19599@pub.cz.oracle.com>\r
+Mail-Followup-To: Kim Minh Kaplan <kimminh.kaplan+nomuch@afnic.fr>,\r
+       Vladimir Marek <vlmarek@volny.cz>, Tomi Ollila <tomi.ollila@iki.fi>,\r
+       notmuch@notmuchmail.org\r
+References: <1366405933-17223-1-git-send-email-Vladimir.Marek@oracle.com>\r
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+Cc: Tomi Ollila <tomi.ollila@iki.fi>, notmuch@notmuchmail.org,\r
+       Vladimir Marek <vlmarek@volny.cz>\r
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+\r
+> You have to somehow instantiate a temporary object, using a function\r
+> call for example.\r
+> \r
+>     #include <string.h>\r
+>     #include <stdio.h>\r
+>     struct example {\r
+>       char data[10];\r
+>       char *c_str() { return data; }\r
+>      example() { strcpy(data, "test"); }\r
+>       ~example() { strcpy(data, "destroyed"); }\r
+>     };\r
+>     example foo()\r
+>     {\r
+>       example res;\r
+>       return res;\r
+>     }\r
+>     main()\r
+>     {\r
+>       printf("%s\n", foo().c_str());\r
+>       char *x = foo().c_str();\r
+>       printf("%s\n", x);\r
+>     }\r
+\r
+Right. After more tests I think I'm getting hang of it. In my examples I\r
+had function similar to\r
+\r
+char *foo() {\r
+  example res;\r
+  return res.c_str();\r
+}\r
+\r
+In this case the reference returned is to _char pointer_ and not to\r
+example struct. So the struct is destroyed before returning from foo to\r
+caller. Compiler does not understand that the returned char pointer does\r
+not have any meaning without the example struct.\r
+\r
+This is where I was doing the mistake, I believe.\r
+\r
+Thank you\r
+-- \r
+       Vlad\r