xutility（2227）：警告C4996：'std :: _ Copy_impl'

Question

I got this warning message.. but i dont know what/where the problem is..!

includes

#pragma warning(push)
#pragma warning(disable:4996) 
#include <boost/archive/iterators/base64_from_binary.hpp>
#include <boost/archive/iterators/insert_linebreaks.hpp>
#include <boost/archive/iterators/transform_width.hpp>
#include <boost/archive/iterators/ostream_iterator.hpp>
#pragma warning(pop)

and the warning

1>c:\program files (x86)\microsoft visual studio 10.0\vc\include\xutility(2227): warning C4996: 'std::_Copy_impl': Function call with parameters that may be unsafe - this call relies on the caller to check that the passed values are correct. To disable this warning, use -D_SCL_SECURE_NO_WARNINGS. See documentation on how to use Visual C++ 'Checked Iterators'
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\xutility(2212): Siehe Deklaration von 'std::_Copy_impl'
1>          c:\users\perlig\documents\visual studio 2010\projects\restmanager\restmanager\**http.cpp(257)**: Siehe Verweis auf die Instanziierung der gerade kompilierten Funktions-template "_OutIt std::copy<boost::archive::iterators::insert_linebreaks<Base,N>,boost::archive::iterators::ostream_iterator<Elem>>(_InIt,_InIt,_OutIt)".
1>          with
1>          [
1>              _OutIt=boost::archive::iterators::ostream_iterator<char>,
1>              Base=boost::archive::iterators::base64_from_binary<boost::archive::iterators::transform_width<const char *,6,8>>,
1>              N=76,
1>              Elem=char,
1>                _InIt=boost::archive::iterators::insert_linebreaks<boost::archive::iterators::base64_from_binary<boost::archive::iterators::transform_width<const char *,6,8>>,76>
1>          ]

the code occur in line 257 as the warning message says. but i´m not able to fix it because i not know what is wrong..

string data contains a "user:password" string for basic auth via http.

http.cpp(257):

// typdef, prepare
using namespace boost::archive::iterators;
stringstream os;
typedef 
    insert_linebreaks<         // insert line breaks every 72 characters
        base64_from_binary<    // convert binary values ot base64 characters
            transform_width<   // retrieve 6 bit integers from a sequence of 8 bit bytes
                const char *,
                6,
                8
            >
        > 
        ,76
    > 
    base64_text; // compose all the above operations in to a new iterator

// encrypt
#pragma warning(push)
#pragma warning(disable:4996)
copy( //<<<<<------ LINE 257
    base64_text(data.c_str()),
    base64_text(data.c_str() + data.size()),
    boost::archive::iterators::ostream_iterator<char>(os)
);
#pragma warning(pop)

anybody got any idea?

Answer 1

I think you know what is the meaning of the warning but first I describe the warning and then say what to do to get rid of it. Microsoft implemented a new security enabled set of function in its CRT, STL, MFC, ... and mark old version of those functions as deprecated to provide a hint for you that you should migrate to new secure version. so it say std::copy is unsafe!! how? as follow:

char storage[ 10 ], *p = storage;
std::copy( std::istream_iterator<int>(std::cin), std::istream_iterator<int>(), p );

Now what will happened if user input more than 10 int? the memory will be overwritten and you corrupted your memory.

Using boost::archive::iterators::ostream_iterator is perfectly safe but since it does not follow the design of safe iterators in MSVC it will considered as unsafe.

Now you should either disable this warning by -D_SCL_SECURE_NO_WARNINGS to cl input flags or add a pragma to disable this warning( as you do ), but why pragma don't work?

the reason is obvious, this pragma work on scope and the scope that you use pragma on it have nothing wrong, you must guard xutility with this pragma and every thing will work as expected.