unary_function<> Structure

說明如何使用 unary_function < > 在 Visual C++ 中的結構。

template<class _A, class _R>
   struct unary_function
   {
      typedef _A argument_type;
      typedef _R result_type;
   };

備註

注意事項
在原型中的類別/參數名稱不相符的標頭檔中的版本。某些已修改以提高可讀性。

unary_function做為基底類別用來進一步定義運算子函式，以下列格式： Result_Typeclassname::運算子x(Argument_Type)。 

範例

// unary_function.cpp
// compile with: /EHsc
//
// Structure used:
//       unary_function<int, float> - allows us
//       to write operator functions accepting an
//       integer and returning floats.
////////////////////////////////////////////

#include <functional>
#include <iostream>

using namespace std ;

/* derive class from unary_function in order to use it */

class unary_test : public unary_function<int,float>
{
public:
  float value;
  unary_test(){value=10.0;}
  unary_test(float x){value=x;}
  result_type operator*(argument_type x);
  result_type operator-(argument_type x);
};

/* You can now easily create operators that accept */
/* an int and return a float.                     */

unary_test::result_type unary_test::operator*(unary_test::argument_type x)
{
  float tmp = value * (float)x;
  cout << "Value after * is " << tmp << endl ;
  return value;
}

unary_test::result_type unary_test::operator-(unary_test::argument_type x)
{
  float tmp = value - (float)x;
  cout << "Value after minus is " << tmp << endl ;
  return tmp;
}

int main(void)
{
  unary_test item;
  unary_test item2(18.0);

  cout << "Begin" << endl ;
  cout.setf(ios::fixed) ;
  item = item * 2;
  item2 = item2 - 5;
}

需求

標頭: <functional>

請參閱

概念

標準樣板程式庫範例