functionobjects.cpp

c++设计思想

//: C08:FunctionObjects.cpp
// From "Thinking in C++, 2nd Edition, Volume 2"
// by Bruce Eckel & Chuck Allison, (c) 2001 MindView, Inc.
// Available at www.BruceEckel.com.
// Using the predefined function object templates
// in the Standard C++ library
//{L} ../TestSuite/Test
// This will be defined shortly:
#include "Generators.h"
#include <algorithm>
#include <vector>
#include <iostream>
#include <functional>
using namespace std;

template<typename T> 
void print(vector<T>& v, char* msg = "") {
  if(*msg != 0)
    cout << msg << ":" << endl;
  copy(v.begin(), v.end(), 
    ostream_iterator<T>(cout, " "));
  cout << endl;
}

template<typename Contain, typename UnaryFunc> 
void testUnary(Contain& source, Contain& dest,
  UnaryFunc f) {
  transform(source.begin(), source.end(), 
    dest.begin(), f);
}

template<typename Contain1, typename Contain2, 
  typename BinaryFunc> 
void testBinary(Contain1& src1, Contain1& src2,
  Contain2& dest, BinaryFunc f) {
  transform(src1.begin(), src1.end(), 
    src2.begin(), dest.begin(), f);
}

// Executes the expression, then stringizes the
// expression into the print statement:
#define T(EXPR) EXPR; print(r, "After " #EXPR);
// For Boolean tests:
#define B(EXPR) EXPR; print(br,"After " #EXPR);

// Boolean random generator:
struct BRand {
  BRand() { srand(time(0)); }
  bool operator()() {
    return rand() > RAND_MAX / 2;
  }
};

int main() {
  const int sz = 10;
  const int max = 50;
  vector<int> x(sz), y(sz), r(sz);
  // An integer random number generator:
  URandGen urg(max);
  generate_n(x.begin(), sz, urg);
  generate_n(y.begin(), sz, urg);
  // Add one to each to guarantee nonzero divide:
  transform(y.begin(), y.end(), y.begin(),
    bind2nd(plus<int>(), 1));
  // Guarantee one pair of elements is ==:
  x[0] = y[0];
  print(x, "x");
  print(y, "y");
  // Operate on each element pair of x & y,
  // putting the result into r:
  T(testBinary(x, y, r, plus<int>()));
  T(testBinary(x, y, r, minus<int>()));
  T(testBinary(x, y, r, multiplies<int>()));
  T(testBinary(x, y, r, divides<int>()));
  T(testBinary(x, y, r, modulus<int>()));
  T(testUnary(x, r, negate<int>()));
  vector<bool> br(sz); // For Boolean results
  B(testBinary(x, y, br, equal_to<int>()));
  B(testBinary(x, y, br, not_equal_to<int>()));
  B(testBinary(x, y, br, greater<int>()));
  B(testBinary(x, y, br, less<int>()));
  B(testBinary(x, y, br, greater_equal<int>()));
  B(testBinary(x, y, br, less_equal<int>()));
  B(testBinary(x, y, br, 
    not2(greater_equal<int>())));
  B(testBinary(x,y,br,not2(less_equal<int>())));
  vector<bool> b1(sz), b2(sz);
  generate_n(b1.begin(), sz, BRand());
  generate_n(b2.begin(), sz, BRand());
  print(b1, "b1");
  print(b2, "b2");
  B(testBinary(b1, b2, br, logical_and<int>()));
  B(testBinary(b1, b2, br, logical_or<int>()));
  B(testUnary(b1, br, logical_not<int>()));
  B(testUnary(b1, br, not1(logical_not<int>())));
} ///:~