c++ - Why won't this code compile? -

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with const, indicated comment, msvc 11 , g++ 4.7.0 refuse compile this:

#include <memory>       // std::unique_ptr #include <utility>      // std::move using namespace std;  struct commandlineargs {     typedef unique_ptr<         wchar_t const* const [],         void(*)( wchar_t const* const* )         > pointerarray;      //pointerarray const  args;         // oops     pointerarray        args;     int const           count;      static wchar_t const* const* parsed(         wchar_t const       commandline[],         int&                count         )     {         return 0;     }      static void deallocate( wchar_t const* const* const p )     {     }      commandlineargs(         wchar_t const   commandline[]   = l"",         int             _               = 0         )         : args( parsed( commandline, _ ), &deallocate )         , count( _ )     {}      commandlineargs( commandlineargs&& other )         : args( move( other.args ) )         , count( move( other.count ) )     {} };  int main() {}

the error messages not seem particularly informative, here's g++'s output:

 main.cpp: in constructor 'commandlineargs::commandlineargs(commandlineargs&&)': main.cpp:38:38: error: use of deleted function 'std::unique_ptr::unique_ptr(const std::unique_ptr&) [w ith _tp = const wchar_t* const; _dp = void (*)(const wchar_t* const*); std::unique_ptr = std::unique_ptr]' in file included c:\program files (x86)\mingw\bin\../lib/gcc/mingw32/4.7.0/include/c++/memory:86:0,                  main.cpp:1: c:\program files (x86)\mingw\bin\../lib/gcc/mingw32/4.7.0/include/c++/bits/unique_ptr.h:402:7: error: declared here

why?

you can not move const object. error because of move constructor.

the unique_ptr, has deleted copy constructor , move constructor declared :

unique_ptr( const unique_ptr & other ); unique_ptr( unique_ptr && other );

since unique_ptr declated const, picks copy constructor, not move constructor.


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