# pointer_to_unary_function<Arg, Result>

Categories: functors, adaptors | Component type: type

### Description

`Pointer_to_unary_function` is a function object adaptor that allows a function pointer `Result (*f)(Arg)` to be treated as an Adaptable Unary Function. 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 Adaptable Unary Function, 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 Unary Function object, and may be passed to an STL algorithm that expects an argument that is a Unary Function. 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 Adaptable Unary Function, 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.

    transform(first, last, first, fabs);

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 adaptable unary function, so we do need to use a `pointer_to_unary_function` adaptor.

    transform(first, last, first,
              compose1(negate<double>, ptr_fun(fabs)));

### 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

Adaptable Unary Function

### Type requirements

- `Arg` is Assignable.
- `Result` is Assignable.

### Public base classes

`unary_function<Arg, Result>`

### Members

Member | Where defined | Description
--- | --- | ---
`argument_type` | Adaptable Unary Function | The type of the function object's argument: `Arg`.
`result_type` | Adaptable Unary Function | The type of the result: `Result`
`result_type operator()(argument_type x)` | Unary Function | 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 Adaptable Unary Function 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`, Adaptable Unary Function

Copyright © 1999 Silicon Graphics, Inc. All Rights Reserved. TrademarkInformation