ptr_fun

ptr_fun

分类： C/C++2012-05-05 20:21 593人阅读 评论(0) 收藏 举报

functionclassfunobjectreturningtypes

 

目录(?)[-]

1. Template parameters
2. Parameters
3. Return value
4. Example

 

转自：http://www.cplusplus.com/reference/std/functional/ptr_fun/

template <class Arg, class Result>
  pointer_to_unary_function<Arg,Result> ptr_fun (Result (*f)(Arg));

template <class Arg1, class Arg2, class Result>
  pointer_to_binary_function<Arg1,Arg2,Result> ptr_fun (Result (*f)(Arg1,Arg2));

Convert function pointer to function object

Returns a function object that encapsulates function f.

Function objects are objects whose class defines member function operator(). This member function allows the object to be used with the same syntax as a regular function call. Several standard algorithms and adaptors are designed to be used with function objects.

It is defined with the same behavior as:

1. template <class Arg, class Result>
2. pointer_to_unary_function<Arg,Result> ptr_fun (Result (*f)(Arg))
3. {
4. return pointer_to_unary_function<Arg,Result>(f);
5. }
6. template <class Arg1, class Arg2, class Result>
7. pointer_to_binary_function<Arg1,Arg2,Result> ptr_fun (Result (*f)(Arg1,Arg2))
8. {
9. return pointer_to_binary_function<Arg1,Arg2,Result>(f);
10. }

Template parameters

Arg, Arg1, Arg2

Types of the function's arguments.

Result

Function's return type.

Parameters

f

Pointer to a function, taking either one argument (of type Arg) or two arguments (of types Arg1 and Arg2) and returning a value of type Result.

Return value

A function object equivalent to f.
pointer_to_unary_function and pointer_to_binary_function are function object types, derived respectively fromunary_function and binary_function.

Example

 

1. // ptr_fun example
2. #include <iostream>
3. #include <functional>
4. #include <algorithm>
5. #include <cstdlib>
6. #include <numeric>
7. using namespace std;
8. int main () {
9. char* foo[] = {"10","20","30","40","50"};
10. int bar[5];
11. int sum;
12. transform (foo, foo+5, bar, ptr_fun(atoi) );
13. sum = accumulate (bar, bar+5, 0);
14. cout << "sum = " << sum << endl;
15. return 0;
16. }

Possible output:

1. sum = 150

ptr_fun使用
转自：http://topic.csdn.net/u/20100112/16/e1973c74-d81c-4e49-bef8-128ab836800b.html

1. // ceshi1.cpp : 定义控制台应用程序的入口点。
2. //
3. #include "stdafx.h"
4. #include <iostream>
5. #include <functional>
6. using std::cout;
7. using std::endl;
8. /*
9. binary_function
10. */
11. template<typename Arg1,typename Arg2,typename Ret>
12. class binary_function{
13. public:
14. typedef Arg1 first_argument_type;
15. typedef Arg2 second_argument_type;
16. typedef Ret return_type;
17. };
18. /*
19. pointer_to_binary_function
20. */
21. template<typename Arg1,typename Arg2,typename Ret>
22. class pointer_to_binary_function:public binary_function<Arg1,Arg2,Ret>{
23. private:
24. Ret (*pmf)(Arg1,Arg2);
25. public:
26. explicit pointer_to_binary_function(Ret (*pmf_)(Arg1,Arg2))
27. :pmf(pmf_){
28. }
29. Ret operator()(Arg1 left,Arg2 right){
30. return pmf(left,right);
31. }
32. };
33. /*
34. ptr_fun
35. */
36. template<typename Arg1,typename Arg2,typename Ret>
37. pointer_to_binary_function<Arg1,Arg2,Ret> ptr_fun(Ret (*pf)(Arg1,Arg2)){
38. return pointer_to_binary_function<Arg1,Arg2,Ret>(pf);
39. }
40. /*
41. test_function
42. */
43. void test_function(int a,int b){
44. cout<<"Arg1 is "<<a<<endl;
45. cout<<"Arg2 is "<<b<<endl;
46. }
47. /*
48. main
49. */
50. int main(int argc,char* argv[]){
51. int a=3;
52. int b=30;
53. (pointer_to_binary_function<int,int,void>(test_function))(a,b);
54. return 0;
55. }