Categories: functors, adaptors | Component type: 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.
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)));
Parameter | Description | Default |
---|---|---|
Arg | The function object's argument type | |
Result | The function object's result type |
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. |
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. |
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