id,summary,reporter,owner,description,type,status,milestone,component,version,severity,resolution,keywords,cc
9578,"Adapters (map_keys, map_values) cause undefined behavior (segv, etc) when applied to R-Values, especially in the context of BOOST_FOREACH",Igor Lubashev <ilubashe@…>,Neil Groves,"When applied to r-values (for example, maps returned by value from a function), adapters do not make a copy of the r-value but just capture a reference to it.  This makes the returned range_iterator dangerous, if it is used after the r-value (the temporary) is destroyed.

In particular, the following use causes undefined behavior on all compilers I'd tested on: g++ (4.1.2, 4.4.3, 4.6.3) and Visual Studio (15 [VC9], 16 [VC10]).

{{{
#!cpp
BOOST_FOREACH(const string &s, return_map_by_value() | map_keys)
  ...
}}}

Note that the following works fine (since BOOST_FOREACH takes care of differentiating between l-values and r-values and does the right thing to r-values):

{{{
#!cpp
BOOST_FOREACH(const MapType::value_type &v, return_map_by_value())
  ...
}}}

It seems that boost::range::adapters need to do a similar thing to what BOOST_FOREACH is does to identify r-values and make a copy (which the compiler is likely to optimize away).


Attached is a test sample and the resulting behavior.
The output is from code compiled with g++ 4.6.3 with no optimizations.

{{{
$ g++ -I ../include/ container_test.cpp
$ ./a.out
Test #1 (local variable)
  Generating map
key = '12345'
key = 'QWERT'
key = 'igor!'
Test #2 (value_type)
  Generating map
key = '12345'
key = 'QWERT'
key = 'igor!'
Test #3 (temp ref)
  Generating map
key = '12345'
key = 'QWERT'
key = 'igor!'
Test #4 (range_iterator)
  Generating map
key = '12345'
key = 'QWERT'
key = 'igor!'
Test #5 (bug)
  Generating map
key = '12345APãr`ãr¨ârãr1 ãrÿÿÿÿABCDE1ãrÿÿÿÿQWERTAâr½™ÿÀâr ârHãr¸ãr1àárÿÿÿÿqwertAärH½™ÿPärärHãr¸ãrAårÐãârxârAÀãrÐãr¨ârãrAÀärX™ÿårÐärHãr¸ãrAäârxârA€ärär¨ârãrA€årؽ™ÿÐårårHãr¸ãrA°ârPåârxârA@årPår¨ârãr
}}}",Bugs,closed,To Be Determined,range,Boost 1.55.0,Problem,duplicate,,ilubashe@…