Luc Bergeron [mailto:bluc@videotron.ca] wrote:
Greets,
I'm trying to use the boost::any component but i'm having
problem with
it !!! I'm using it because I need a way to store parameters of
different type. That real fine but I can't retrieve the value
from the
boost::any. This is what i've tried :
std::string GetStringFromAny(const boost::any& val) const
{
std::string strVal;
try
{
strVal = boost::any_caststd::string(val);
}
catch(boost::bad_any_cast &err)
{
std::cerr << err.what() << std::endl;
return "";
}
return strVal;
}
But I always have a bad_any_cast exception. From the
documentation, at
leats what I understand of it, "If passed a value or reference, it
returns a copy of the value content if successful". Can
someone point me
in the right direction as to how can I extract the value within a
boost::any type, I think i'm lost !!! :)
The following program works for me, without any error (using MSVC6):
#include
#include <string>
#include <iostream>
std::string GetStringFromAny(const boost::any& val)
{
std::string strVal;
try
{
strVal = boost::any_caststd::string(val);
}
catch(boost::bad_any_cast &err)
{
std::cerr << err.what() << std::endl;
return "";
}
return strVal;
}
int main()
{
boost::any anAny( std::string("Hello, world") );
std::string converted = GetStringFromAny( anAny );
std::cout << "Converted: [" << converted << "]" << std::endl;
}
The output, as I expected, was:
Converted: [Hello, world]
Note that if I add more to main:
int main()
{
boost::any anAny( std::string("Hello, world") );
std::string converted = GetStringFromAny( anAny );
std::cout << "Converted: [" << converted << "]" << std::endl;
anAny = 23;
converted = GetStringFromAny( anAny );
std::cout << "Converted: [" << converted << "]" << std::endl;
}
the second conversion fails. The conversion will only succeed if the type
that boost::any currently holds can be implicitly converted into the type
you want to retrieve. If you want to convert from (for example) an int to a
string, you'll need boost::lexical_cast.
--
Jim
--
Jim
