reference to const static object variable

[Bob Doe]

I have a const static object. What is the right syntax to get a
reference to the std::vector within the std::map variable?:

class MyObj
{
public:
...
std::map<std::s tring,
std::vector<std ::string l_;
};

static MyObj obj;

int main()
{
...
const std::vector<std ::string&regexL ist = obj.l_["key"]; //
compiler error
...
};

[Obnoxious User]

Re: reference to const static object variable

On Fri, 14 Nov 2008 11:23:28 -0800, Bob Doe wrote:

I have a const static object. What is the right syntax to get a
reference to the std::vector within the std::map variable?:
>
class MyObj
{
public:
...
std::map<std::s tring,
std::vector<std ::string l_;
};
>
static MyObj obj;
>
int main()
{
...
const std::vector<std ::string&regexL ist = obj.l_["key"]; //
compiler error
...
};

Did you care to read the error message? What did it say?

--
OU
Remember 18th of June 2008, Democracy died that afternoon.

http://frapedia.se/wiki/Information_in_English

[Bob Doe]

Re: reference to const static object variable

sorry,

The example should have been:

class MyObj
{
public:
MyObj()
{
std::vector<std ::stringt;
t.push_back("zz z");
l_["a"] = t;
}

std::map<std::s tring,
std::vector<std ::string l_;
};

const static MyObj obj;

int main()
{
const std::vector<std ::string&regexL ist = obj.l_["key"];
}


-----
I want to maintain the const-ness of MyObj, and have read access to
the std::vector within std::map...

and the error message says:

passing `const
map<basic_strin g<char,string_c har_traits<char >,__default_all oc_template<fal se,
0>

>,vector<basic_ string<char,str ing_char_traits <char>,__defaul t_alloc_templat e<false,

0>

>,allocator<bas ic_string<char, string_char_tra its<char>,__def ault_alloc_temp late<false,

0 >

>,less<basic_st ring<char,strin g_char_traits<c har>,__default_ alloc_template< false,

0

>,allocator<vec tor<basic_strin g<char,string_c har_traits<char >,__default_all oc_template<fal se,

0>

>,allocator<bas ic_string<char, string_char_tra its<char>,__def ault_alloc_temp late<false,

0 ' as `this' argument of `class
vector<basic_st ring<char,strin g_char_traits<c har>,__default_ alloc_template< false,
0>

>,allocator<bas ic_string<char, string_char_tra its<char>,__def ault_alloc_temp late<false,

0 &
map<basic_strin g<char,string_c har_traits<char >,__default_all oc_template<fal se,
0>

>,vector<basic_ string<char,str ing_char_traits <char>,__defaul t_alloc_templat e<false,

0>

>,allocator<bas ic_string<char, string_char_tra its<char>,__def ault_alloc_temp late<false,

0 >

>,less<basic_st ring<char,strin g_char_traits<c har>,__default_ alloc_template< false,

0

>,allocator<vec tor<basic_strin g<char,string_c har_traits<char >,__default_all oc_template<fal se,

0>

>,allocator<bas ic_string<char, string_char_tra its<char>,__def ault_alloc_temp late<false,

0 ::operator [](const string &)' discards qualifiers


Which I don't understand.

const static MyObj obj;

On Nov 14, 12:30 pm, Obnoxious User <O...@127.0.0.1 wrote:

On Fri, 14 Nov 2008 11:23:28 -0800, Bob Doe wrote:

I have a const static object.  What is the right syntax to get a
reference to the std::vector within the std::map variable?:

>

class MyObj
{
   public:
     ...
     std::map<std::s tring,
                  std::vector<std ::string l_;
};

>

 static MyObj obj;

>

int main()
{
  ...
  const std::vector<std ::string&regexL ist = obj.l_["key"];  //
compiler error
  ...
};

>
Did you care to read the error message? What did it say?
>
--
OU
Remember 18th of June 2008, Democracy died that afternoon.http://frapedia..se/wiki/Information_in_English

[James Kanze]

Re: reference to const static object variable

On Nov 14, 10:24 pm, Bob Doe <DumpForJ...@gm ail.comwrote:

sorry,

The example should have been:

class MyObj
{
   public:
      MyObj()
      {
         std::vector<std ::stringt;
         t.push_back("zz z");
         l_["a"] = t;
      }

      std::map<std::s tring,
               std::vector<std ::string l_;
};

const static MyObj obj;

int main()
{
   const std::vector<std ::string&regexL ist = obj.l_["key"];

Have you looked at the documentation of std::map<>:oper ator[]?
What does it do?

Since it modifies the map, you can't use it on a const object.

}

I want to maintain the const-ness of MyObj, and have read
access to the std::vector within std::map...

Then operator[] isn't the function you want. Something like:


std::map< std::string, std::vector< std::string >

>::const_iterat or

entry = obj.l_[ "key" ] ;
if ( entry != obj.l_.end() ) {
std::vector< std::string const&
regexList = entry->second ;
// ...
}

maybe. (Or maybe std::map isn't what you really want, except
buried deep in the implementation of something with a more
congenial interface.)

--
James Kanze (GABI Software) email:james.kan ze@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientier ter Datenverarbeitu ng
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34

[Obnoxious User]

Re: reference to const static object variable

On Fri, 14 Nov 2008 14:59:46 -0800, James Kanze wrote:

On Nov 14, 10:24 pm, Bob Doe <DumpForJ...@gm ail.comwrote:

>sorry,

>

[snip]

>

>I want to maintain the const-ness of MyObj, and have read access to the
>std::vector within std::map...

>
Then operator[] isn't the function you want. Something like:
>
>
std::map< std::string, std::vector< std::string >

>>::const_itera tor

entry = obj.l_[ "key" ] ;

const_iterator entry = obj.find("key") ;

if ( entry != obj.l_.end() ) {
std::vector< std::string const&
regexList = entry->second ;
// ...
}
>

--
OU
Remember 18th of June 2008, Democracy died that afternoon.

http://frapedia.se/wiki/Information_in_English

[James Kanze]

Re: reference to const static object variable

On Nov 15, 9:11 am, Obnoxious User <O...@127.0.0.1 wrote:

On Fri, 14 Nov 2008 14:59:46 -0800, James Kanze wrote:

On Nov 14, 10:24 pm, Bob Doe <DumpForJ...@gm ail.comwrote:

sorry,

[snip]

I want to maintain the const-ness of MyObj, and have read
access to the std::vector within std::map...

Then operator[] isn't the function you want.  Something like:

    std::map< std::string, std::vector< std::string >

>::const_iterat or

                        entry = obj.l_[ "key"] ;

const_iterator entry = obj.find("key") ;

Yes, obviously.

    if ( entry != obj.l_.end() ) {
        std::vector< std::string const&
                            regexList = entry->second ;
        // ...
    }

--
James Kanze (GABI Software) email:james.kan ze@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientier ter Datenverarbeitu ng
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34