c++ - lambda: should capturing const reference by reference yield undefined behaviour? -

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i found nasty bug in code because captured const reference string reference. time lambda run original string object long gone , referenced value empty whereas purpose contains value of original string, hence bug.

what baffles me did not invoke crash @ runtime: after all, shouldn't undefined behaviour since afaik there dangling reference? when looking @ id under debugger, doesn't garbage constructed empty string.

here's test case; prints empty line:

typedef std::vector< std::function< void() > > functions;  void addfunction( const std::string& id, functions& funs ) {   funs.push_back( [&id] ()     {         //the type of id const std::string&, there         //is no object reference. ub?       std::cout << id << std::endl;     } ); }  int main() {   functions funs;   addfunction( "id", funs );   funs[ 0 ](); }

undefined behavior means there no requirement should happen. there no requirement should crash. whatever memory dangling reference points at, there's no reason shouldn't contain looks empty string, , it's plausible destructor of string leaves memory in state.


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