composefinal.cpp

来自「Thinking in C++(Second Editon)」· C++ 代码 · 共 51 行

//: C06:ComposeFinal.cpp {-edg}
// From "Thinking in C++, Volume 2", by Bruce Eckel & Chuck Allison.
// (c) 1995-2004 MindView, Inc. All Rights Reserved.
// See source code use permissions stated in the file 'License.txt',
// distributed with the code package available at www.MindView.net.
// An adaptable composer.
#include <algorithm>
#include <cassert>
#include <cstdlib>
#include <functional>
#include <iostream>
#include <iterator>
#include <string>
#include <vector>
#include "NumStringGen.h"
using namespace std;

template<typename F1, typename F2> class unary_composer
: public unary_function<typename F2::argument_type,
                        typename F1::result_type> {
  F1 f1;
  F2 f2;
public:
  unary_composer(F1 f1, F2 f2) : f1(f1), f2(f2) {}
  typename F1::result_type
  operator()(typename F2::argument_type x) {
    return f1(f2(x));
  }
};

template<typename F1, typename F2>
unary_composer<F1, F2> compose(F1 f1, F2 f2) {
  return unary_composer<F1, F2>(f1, f2);
}

int main() {
  const int SZ = 9;
  vector<string> vs(SZ);
  // Fill it with random number strings:
  generate(vs.begin(), vs.end(), NumStringGen());
  copy(vs.begin(), vs.end(),
    ostream_iterator<string>(cout, "\t"));
  cout << endl;
  vector<double> vd;
  transform(vs.begin(), vs.end(), back_inserter(vd),
    compose(ptr_fun(atof), mem_fun_ref(&string::c_str)));
  copy(vd.begin(), vd.end(),
    ostream_iterator<double>(cout, "\t"));
  cout << endl;
} ///:~