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| 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 typedefs 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 backward-compatibility 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
