

 
Categories: functors, adaptors  Component type: type 
Description
Pointer_to_unary_function
is a functors adaptor that allows a function pointer Result (*f)(Arg)
to be treated as an AdaptableUnaryFunction. That is: if F
is a pointer_to_unary_function<Arg, Result>
that was initialized with an underlying function pointer f
of type Result (*)(Arg)
, then F(x)
calls the function f(x)
. The difference between f
and F
is that pointer_to_unary_function
is an AdaptableUnaryFunction, i.e. it defines the nested typedef
s argument_type
and result_type
.
Note that a function pointer of type Result (*)(Arg)
is a perfectly good UnaryFunction object, and may be passed to an STL algorithm that expects an argument that is a UnaryFunction. The only reason for using the pointer_to_unary_function
object is if you need to use an ordinary function in a context that requires an AdaptableUnaryFunction, e.g. as the argument of a function object adaptor.
Most of the time, you need not declare an object of type pointer_to_unary_function
directly. It is almost always easier to construct one using the ptr_fun
function.
Example
The following code fragment replaces all of the numbers in a range with their absolute values, using the standard library function fabs
. There is no need to use a pointer_to_unary_function
adaptor in this case.
The following code fragment replaces all of the numbers in a range with the negative of their absolute values. In this case we are composing fabs
and negate
. This requires that fabs
be treated as an AdaptableUnaryFunction, so we do need to use a pointer_to_unary_function
adaptor.
Definition
Defined in the standard header functional, and in the nonstandard backwardcompatibility header function.h.
Template parameters
Parameter  Description  Default 
Arg  The function object's argument type  
Result  The function object's result type  
Model of
AdaptableUnaryFunction
Type requirements
Public base classes
unary_function<Arg, Result>
Members
Member  Where defined  Description 
argument_type  AdaptableUnaryFunction  The type of the function object's argument: Arg . 
result_type  AdaptableUnaryFunction  The type of the result: Result 
result_type operator()(argument_type x)  UnaryFunction  Function call operator. 
pointer_to_unary_function(Result (*f)(Arg))  pointer_to_unary_function  See below. 
pointer_to_unary_function()  pointer_to_unary_function  See below. 
template <class Arg, class Result>
pointer_to_unary_function<Arg, Result>
ptr_fun(Result (*x)(Arg));
 pointer_to_unary_function  See below. 
New members
These members are not defined in the AdaptableUnaryFunction requirements, but are specific to pointer_to_unary_function
.
Member  Description 
pointer_to_unary_function(Result (*f)(Arg))  The constructor. Creates a pointer_to_unary_function whose underlying function is f . 
pointer_to_unary_function()  The default constructor. This creates a pointer_to_unary_function that does not have an underlying C function, and that therefore cannot actually be called. 
template <class Arg, class Result>
pointer_to_unary_function<Arg, Result>
ptr_fun(Result (*x)(Arg));
 If f is of type Result (*)(Arg) then ptr_fun(f) is equivalent to pointer_to_unary_function<Arg,Result>(f) , but more convenient. This is a global function, not a member. 
Notes
See also
pointer_to_binary_function
, ptr_fun
, AdaptableUnaryFunction