Re: [Boost-users] [bind] static array vs. pointer vector

From: Daniel (boost_at_[hidden])
Date: 2007-03-26 16:11:06

> Date: Mon, 26 Mar 2007 11:24:08 -0400
> From: "Christian Henning" <chhenning_at_[hidden]>
> Subject: [Boost-users] [bind] static array vs. pointer vector
> To: boost-users_at_[hidden]
> Message-ID:
> 	<949801310703260824n31c76204pcd63bb686169e15c_at_[hidden]>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> Hi there, I have posted this question last Friday, already. But maybe
> my example was too confusing. Here is a more simple example.
> Basically, I don't see what the big difference is when using
> boost::bind with a pointer vector ( std::vector<info*> ) and a static
> array of info.
>
> Please consider the following code:
>
> #include <string>
> #include <algorithm>
> #include <functional>
> #include <vector>
>
> #include <boost/bind.hpp>
>
> using namespace std;
> using namespace boost;
>
> struct info
> {
>   int    a;
>   string s;
> };
>
> static info table[] =
> {
>   { 16, "Hello" },
>   { 18, "Moin" }
> };
>
> string& get_s( info* p )
> {
>   return p->s;
> }
>
> int _tmain(int argc, _TCHAR* argv[])
> {
>   {
>      vector<info*> v;
>      find_if( v.begin(), v.end()
>              , bind( equal_to<string>()
>                    , bind( &get_s, _1 )
>                    , "Moin" ));
>   }
>
>   {
>      find_if( &table[0], &table[0] + 2
>             , bind( equal_to<string>()
>                   , bind( &get_s, _1 )
>                   , "Moin" ));
>
>   }
> }
>
> The second find_if wont complie using MSVC 7.1. The errors are:
>
> c:\boost\boost\bind.hpp(219) : error C2664: 'std::string &(info *)' :
> cannot convert parameter 1 from 'info' to 'info *'
[snip]
>
> Any ideas?
>
> Christian

In 1st case, when you dereference vector<info*> iterator, you will get 
info* pointer. But in 2nd case, your iterator is info* pointer, so you 
get info object when you dereference it. This is also mentioned at 
beginning of error message - "cannot convert parameter 1 from 'info' to 
'info *'". Therefore you should change your get_s() function to accept 
info (or info&), or your binding expression to convert info to info*.

Daniel