Homework-17

hw17/enableifSort.cpp

+#include<iostream>
+#include<array>
+#include<list>
+#include<iterator>
+#include<type_traits>
+
+using namespace std;
+/*
+template<class T, enable_if_t<is_arithmetic_v<T>> * = nullptr>
+T
+foo(T t) {
+  return t*t;
+}
+
+int main() {
+  int  a = 10;
+  cout << foo(a) << endl;
+  return 0;
+}
+*/
+template<typename T, enable_if_t<is_same_v<typename iterator_traits<T>::iterator_category, random_access_iterator_tag>> * = nullptr>
+void
+mySort(T beg, T end) {
+  cout << "Sort->random_access_iterator" << endl;
+}
+
+template<typename T, enable_if_t<is_same_v<typename iterator_traits<T>::iterator_category, forward_iterator_tag>> * = nullptr>
+void
+mySort(T beg, T end) {
+  cout << "Sort->forward_iterator" << endl;
+}
+
+template<typename T, enable_if_t<is_same_v<typename iterator_traits<T>::iterator_category, bidirectional_iterator_tag>> * = nullptr>
+void
+mySort(T beg, T end) {
+  cout << "Sort->bidirectional_iterator" << endl;
+}
+
+int main() {
+  array<int, 3> a = {3, 2, 1};
+  list<int> b = {3, 2, 1};
+  
+  mySort(a.begin(), a.end());
+  mySort(b.begin(), b.end());
+  
+  return 0;
+}
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hw17/os_joiner.cpp

+#include<boost/function_output_iterator.hpp>
+#include<iostream>
+#include<string>
+#include<vector>
+
+template<typename T, typename t>
+class ostream_joiner {
+public:
+  ostream_joiner(T& s, t c)
+    : m_str(&s), delim(c) {}
+
+  void operator()(const T& x) {
+    if(!is_first) {
+      std::cout << delim << x;
+    }
+    else {
+      std::cout << x;
+      is_first = false;
+    }
+  }
+private:
+  T* m_str;
+  t delim;
+  bool is_first = true;
+};
+
+int main(int, char*[])
+{
+  std::vector<std::string> x1;
+  x1.push_back("hello");
+  x1.push_back("world");
+  
+  std::string s1 = "";
+  std::string c1 = ",";
+  ostream_joiner o1(s1, c1);
+  
+  std::copy(x1.begin(), x1.end(),
+            boost::make_function_output_iterator(o1));
+
+  std::cout << std::endl;
+
+  std::vector<int> x2;
+  x2.push_back(2);
+  x2.push_back(3);
+
+  int s2;
+  std::string c2 = ":";
+  ostream_joiner o2(s2, c2);
+  
+  std::copy(x2.begin(), x2.end(),
+            boost::make_function_output_iterator(o2));
+
+  std::cout << std::endl;
+
+  return 0;
+}
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hw17/tostring.cpp

+#include<iostream>
+#include<iomanip>
+#include<string>
+
+using namespace std;
+
+class student {
+public:
+  student(string n, int a): name(n), age(a) {}
+  string name;
+  int age;
+};
+
+int main() {
+  int byte = 255;
+  double x = 2.3;;
+  cout << to_string(byte) << endl;
+//  cout << to_string(hex, uppercase, byte) << endl;
+  cout << to_string(0 - 0) << endl;
+  cout << to_string(false) << endl;
+  cout << setw(10) << to_string(x) << endl;
+  
+  student s1("Einstein", 30);
+  cout << s1.name << " " << s1.age << endl;
+//  cout << to_string(s1) << endl;
+  
+/*
+  I tried both std::to_string and generic to_string. From my limited experience, I think std::to_string is quite useful when we convert a val(int/double) to string representation. The generic to_string function to me is a combination of std::to_string and std::cout. In my opinion, for std::to_string, we can not trace back to the input type. For example std::to_string(0 - 0) and std::to_string(false) both have the same output "0". But the generic to_string, we have this ability to trace back to the input type and I hope this is an advantage in some case.
+*/
+  
+  return 0;
+}
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