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

26 Mar 2007


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Date: Mon, 26 Mar 2007 11:24:08 -0400
From: "Christian Henning" 
Subject: [Boost-users] [bind] static array vs. pointer vector
To: boost-users@lists.boost.org
Message-ID:
  <949801310703260824n31c76204pcd63bb686169e15c@mail.gmail.com>
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 ) and a static
array of info.
Please consider the following code:
#include <string>
#include <algorithm>
#include <functional>
#include <vector>
#include 
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 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 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