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+Date: Tue, 30 Apr 2013 10:48:52 +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: <20130430084852.GA19599@pub.cz.oracle.com>\r
+Mail-Followup-To: Kim Minh Kaplan <kimminh.kaplan+nomuch@afnic.fr>,\r
+ Tomi Ollila <tomi.ollila@iki.fi>, notmuch@notmuchmail.org,\r
+ Vladimir Marek <vlmarek@volny.cz>\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
+\r
+--J/dobhs11T7y2rNN\r
+Content-Type: text/plain; charset=utf-8\r
+Content-Disposition: inline\r
+Content-Transfer-Encoding: 8bit\r
+\r
+Hi,\r
+\r
+Thank you, I found it eventually too. But I wrote little test program\r
+(attached) which confused me. I haven't had much time to take a look\r
+into it since weekend.\r
+\r
+The idea is to have temporary object where I can detect whether\r
+destructor was called.\r
+\r
+I thought that\r
+\r
+printf ("%s\n", s.c_str());\r
+will print "test"\r
+\r
+and\r
+\r
+x=s.c_str();\r
+printf ("%s\n", x);\r
+\r
+will print "destroyed"\r
+\r
+On my machine both prints "destroyed".\r
+\r
+\r
+I still believe my fix is correct, but I'm not at the position to be\r
+able to defend it at the moment :)\r
+\r
+Thank you\r
+-- \r
+ Vlad\r
+\r
+> The january 2012 working draft: \r
+> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3337.pdf\r
+> \r
+> 12.2 Temporary objects [class.temporary]\r
+> \r
+> 1 Temporaries of class type are created in various contexts: binding a\r
+> reference to a prvalue (8.5.3), returning a prvalue (6.6.3) […]\r
+> \r
+> 3 When an implementation introduces a temporary object of a class that\r
+> has a non-trivial constructor (12.1, 12.8), it shall ensure that a\r
+> constructor is called for the temporary object. Similarly, the\r
+> destructor shall be called for a temporary with a non-trivial destructor\r
+> (12.4). Temporary objects are destroyed as the last step in evaluating\r
+> the full-expression (1.9) that (lexically) contains the point where they\r
+> were created.\r
+\r
+--J/dobhs11T7y2rNN\r
+Content-Type: text/plain; charset=utf-8\r
+Content-Disposition: attachment; filename="a.cc"\r
+\r
+#include <stdio.h>\r
+#include <vector>\r
+#include <string.h>\r
+\r
+using namespace std;\r
+\r
+class array {\r
+ vector<char> impl;\r
+\r
+ public:\r
+\r
+ array(int size):impl(size) { }\r
+ array(array &in):impl(in.impl) { }\r
+\r
+ char*\r
+ operator[](size_t i) {\r
+ return &impl[i];\r
+ };\r
+\r
+ ~array() {\r
+ strcpy(&impl[0], "destroyed");\r
+ }\r
+};\r
+\r
+class str {\r
+ array tmp;\r
+\r
+ public:\r
+\r
+ str(const char *input):tmp(100) {\r
+ strcpy(tmp[0], input);\r
+ };\r
+\r
+ const char* c_str() {\r
+ return (array(tmp))[0];\r
+ };\r
+};\r
+\r
+\r
+int\r
+main (int argc, char **argv)\r
+{\r
+ str s("test");\r
+ const char *x;\r
+ printf ("%s\n", s.c_str());\r
+ x=s.c_str();\r
+ printf ("%s\n", x);\r
+ return 0;\r
+}\r
+\r
+--J/dobhs11T7y2rNN--\r
projects / notmuch-archives.git / commitdiff