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bind2nd (3)
  • >> bind2nd (3) ( Solaris man: Библиотечные вызовы )
  • 
                           Standard C++ Library
                 Copyright 1998, Rogue Wave Software, Inc.
    
    
    NAME
         bind1st, bind2nd, binder1st, binder2nd
    
          - Templatized utilities to bind values to function objects.
    
    
    
    SYNOPSIS
         #include <functional>
         template <class Operation>
         class binder1st : public unary_function<typename
                           Operation::second_argument_type,
                           typename Operation::result_type> ;
    
         template <class Operation, class T>
         binder1st<Operation> bind1st (const Operation&, const T&);
         template <class Operation>
         class binder2nd : public unary_function<typename
                           Operation::first_argument_type,
                           typename Operation::result_type> ;
    
         template <class Operation, class T>
         binder2nd<Operation> bind2nd (const Operation&, const T&);
    
    
    
    DESCRIPTION
         Because so many functions included in the  standard  library
         take  other  functions  as  arguments,  the library includes
         classes that let you build new function objects out  of  old
         ones.  Both  bind1st() and bind2nd() are functions that take
         as arguments a binary function object f and a value  x,  and
         return,  respectively,  classes binder1st and binder2nd. The
         underlying  function  object   must   be   a   subclass   of
         binary_function.
    
         Class binder1st binds the value to the first argument of the
         binary  function,  and binder2nd does the same thing for the
         second argument of the function. The resulting  classes  can
         be  used  in  place  of  a unary predicate in other function
         calls.
    
         For example, you could use the count_if algorithm  to  count
         all  elements  in a vector that are less than or equal to 7,
         using the following:
    
         count_if (v.begin, v.end, bind1st(greater<int> (),7),
                   littleNums)
    
         This function adds one to littleNums each time the predicate
         is  true,  in  other  words, each time 7 is greater than the
         element.
    
    
    
    INTERFACE
         // Class binder1st
         template <class Operation>
         class binder1st
            : public unary_function<typename
                                   Operation::second_argument_type,
                                   typename Operation::result_type>
         {
         public:
    
           binder1st(const Operation&,
                     const typename
                     Operation::first_argument_type&);
           typename Operation::result_type operator()
                    (const typename Operation::second_argument_type&)
                    const;
         };
    
         // Class binder2nd
         template <class Operation>
         class binder2nd
            : public unary_function<typename
                                   Operation::first_argument_type,
                                   typename Operation::result_type>
         {
         public:
    
           binder2nd(const Operation&,
                     const typename
                     Operation::second_argument_type&);
           typename Operation::result_type operator()
                    (const typename Operation::first_argument_type&)
                    const;
         };
    
         // Creator bind1st
    
           template <class Operation, class T>
           binder1st<Operation> bind1st (const Operation&,
                                         const T&);
    
         // Creator bind2nd
           template<class Operation, class T>
           binder2nd <Operation> bind2nd(const Operation&,
                                         const T&);
    
    
    
    EXAMPLE
         //
         // binders.cpp
         //
          #include <functional>
          #include <algorithm>
          #include <vector>
          #include <iostream>
         using namespace std;
         int main()
          {
           typedef vector<int>::iterator iterator;
           int d1[4] = {1,2,3,4};
            //
            // Set up a vector
            //
           vector<int> v1(d1,d1 + 4);
            //
            // Create an 'equal to 3' unary predicate by binding 3 to
            // the equal_to binary predicate.
            //
           binder1st<equal_to<int> > equal_to_3 =
              bind1st(equal_to<int>(),3);
            //
            // Now use this new predicate in a call to find_if
            //
           iterator it1 = find_if(v1.begin(),v1.end(),equal_to_3);
            //
            // Even better, construct the new predicate on the fly
            //
           iterator it2 =
              find_if(v1.begin(),v1.end(),bind1st(equal_to<int>(),3));
            //
            // And now the same thing using bind2nd
            // Same result since == is commutative
            //
           iterator it3 =
              find_if(v1.begin(),v1.end(),bind2nd(equal_to<int>(),3));
            //
            // it3 = v1.begin() + 2
            //
            // Output results
            //
           cout << *it1 << " " << *it2 << " " << *it3 << endl;
           return 0;
    
          }
    
         Program Output
    
    
    
         3 3 3
    
    
    
    WARNINGS
         If your compiler does not support default  template  parame-
         ters,  then you always need to supply the Allocator template
         argument. For instance, you have to write:
    
         vector<int,allocator<int> >
    
         instead of:
    
         vector<int>
    
         If your compiler does not support namespaces,  then  you  do
         not need the using declaration for std.
    
    
    
    SEE ALSO
         Function_Objects
    
    
    
    


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