问题
I am trying to use boost::bind
and STL with boost::tuple
, but each time I try to compile I get the following error.
error: call of overloaded ‘bind(<unresolved overloaded function type>,
boost::arg<1>&)’ is ambiguous
Do you know what I am doing wrong here and why is only for the boost::arg<1>
?
Thanks AFG
#include <iostream>
#include <algorithm>
#include <vector>
#include <cstdio>
#include <boost/tuple/tuple.hpp>
#include <boost/assign.hpp>
#include <boost/bind.hpp>
int main( int argc, const char** argv ){
using namespace boost::assign;
typedef boost::tuple< int, double > eth_array;
std::vector< eth_array > v;
v+= boost::make_tuple( 10,23.4), boost::make_tuple( 12,24.4) );
std::for_each( v.begin()
, v.end()
, boost::bind<int>(
printf
, "%d-%f"
, boost::bind( eth_array::get<0>, _1 )
, boost::bind( eth_array::get<1>, _1 )
)
);
回答1:
The get
function has more than one template parameter: in addition to the index, it is also parameterized on the content of the tuple (the head and the tail of the cons
).
Consequently, get<0>
is not an instantiation of the template; you need to provide the additional arguments:
typedef eth_array::head_type head;
typedef eth_array::tail_type tail;
... get<0, head, tail> ...
However, this still won't work because get
is overloaded (const and non-const version), so you need to explicitely state which overload you want. To do so, you need to use a function pointer with the correct type:
// const version of get, which takes and returns const references
int const & (*get0)( boost::tuples::cons<head, tail> const & ) =
boost::get<0, head, tail>;
double const & (*get1)( boost::tuples::cons<head, tail> const & ) =
boost::get<1, head, tail>;
Now you can use these function pointers in your bind expression:
std::for_each( v.begin(),
v.end(),
boost::bind<int>(
printf,
"%d-%f",
boost::bind( get0, _1 ),
boost::bind( get1, _1 )
)
);
// outputs 10-23.40000012-24.400000
As you can see, overloaded function templates and bind
does not get along very well...
回答2:
Several problems here:
eth_array
not defined, I'm guessing that should be _array.
v+= ( boost::make_tuple( 10,23.4) )( boost::make_tuple( 12,24.4) );
Here you are trying to call the tuple as a function? Maybe you tried something like:
v+=boost::make_tuple( 10,23.4);
v+=boost::make_tuple( 12,24.4);
Finally, what seems to be causing the issue you described:
boost::bind( eth_array::get<0>, _1 )
You should try using a function pointer instead of raw function name:
boost::bind( ð_array::get<0>, _1 )
The complete body of main() that I got to compile and run:
int main( int argc, const char** argv ){
using namespace boost::assign;
typedef boost::tuple< int, double > _array;
std::vector< _array > v;
v+=boost::make_tuple( 10,23.4);
v+=boost::make_tuple( 12,24.4);
std::for_each( v.begin()
, v.end()
, boost::bind<int>(
printf
, "%d-%f\n"
, boost::bind( &_array::get<0>, _1 )
, boost::bind( &_array::get<1>, _1 )
)
);
}
来源:https://stackoverflow.com/questions/7157210/boostbind-doesnt-work-with-boosttuplegetn