From 023e41a5af4d50bc3825429c74ca17705d8ca120 Mon Sep 17 00:00:00 2001
From: pezy <urbancpz@gmail.com>
Date: Fri, 15 Sep 2017 00:39:03 +0800
Subject: [PATCH] try to give a solution of #135

---
 .gitignore            |  3 ++
 ch16/ex16.41/main.cpp | 30 --------------
 ch16/ex16_41_sum.cpp  | 92 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 95 insertions(+), 30 deletions(-)
 delete mode 100644 ch16/ex16.41/main.cpp
 create mode 100644 ch16/ex16_41_sum.cpp

diff --git a/.gitignore b/.gitignore
index e84bed97..c8a168df 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,6 @@
+#vscode
+.vs
+
 # Mac OS
 .DS_Store
 
diff --git a/ch16/ex16.41/main.cpp b/ch16/ex16.41/main.cpp
deleted file mode 100644
index 2b6a0732..00000000
--- a/ch16/ex16.41/main.cpp
+++ /dev/null
@@ -1,30 +0,0 @@
-/***************************************************************************
- *  @file       main.cpp
- *  @author     Alan.W
- *  @date       07  Feb 2014
- *  @remark     This code is for the exercises from C++ Primer 5th Edition
- *  @note
- ***************************************************************************/
-//!
-//! Exercise 16.41:
-//! Write a version of sum with a return type that is guaranteed to be large
-//! enough to hold the result of the addition.
-//!
-
-
-#include <iostream>
-#include <vector>
-#include <string>
-
-template<typename T>
-auto sum(T lhs, T rhs) -> decltype( lhs + rhs)
-{
-    return lhs + rhs;
-}
-
-int main()
-{
-    auto s= sum(123456789123456789123456789123456789123456789, 123456789123456789123456789123456789123456789) ;
-    ;
-    ;
-}
diff --git a/ch16/ex16_41_sum.cpp b/ch16/ex16_41_sum.cpp
new file mode 100644
index 00000000..d0428ed2
--- /dev/null
+++ b/ch16/ex16_41_sum.cpp
@@ -0,0 +1,92 @@
+#include <climits>
+#include <iostream>
+
+template <typename T> struct promote;
+
+template <> struct promote<short int> {
+    using type = int;
+};
+
+template <> struct promote<unsigned short int> {
+    using type = unsigned int;
+};
+
+template <> struct promote<int> {
+    using type = long long int;
+};
+
+template <> struct promote<unsigned int> {
+    using type = unsigned long int;
+};
+
+template <> struct promote<long int> {
+    using type = long long int;
+};
+
+template <> struct promote<unsigned long int> {
+    using type = unsigned long int;
+};
+
+template <> struct promote<long long int> {
+    using type = unsigned long long int;
+};
+
+template <> struct promote<unsigned long long int> {
+    using type = unsigned long long int;
+};
+
+template <> struct promote<float> {
+    using type = double;
+};
+
+template <> struct promote<double> {
+    using type = long double;
+};
+
+template <> struct promote<long double> {
+    using type = long double;
+};
+
+template <typename T> using promote_t = typename promote<T>::type;
+
+template <typename T> auto sum(T lhs, T rhs) -> promote_t<T>
+{
+    return static_cast<promote_t<T>>(lhs) + rhs;
+}
+
+int main()
+{
+    std::cout << sum(std::numeric_limits<short int>::max(),
+                     std::numeric_limits<short int>::max())
+              << std::endl;
+    std::cout << sum(std::numeric_limits<unsigned short int>::max(),
+                     std::numeric_limits<unsigned short int>::max())
+              << std::endl;
+    std::cout << sum(std::numeric_limits<int>::max(),
+                     std::numeric_limits<int>::max())
+              << std::endl;
+    std::cout << sum(std::numeric_limits<unsigned int>::max(),
+                     std::numeric_limits<unsigned int>::max())
+              << std::endl;
+    std::cout << sum(std::numeric_limits<long int>::max(),
+                     std::numeric_limits<long int>::max())
+              << std::endl;
+    std::cout << sum(std::numeric_limits<unsigned long int>::max(),
+                     std::numeric_limits<unsigned long int>::max())
+              << std::endl;
+    std::cout << sum(std::numeric_limits<long long int>::max(),
+                     std::numeric_limits<long long int>::max())
+              << std::endl;
+    std::cout << sum(std::numeric_limits<unsigned long long int>::max(),
+                     std::numeric_limits<unsigned long long int>::max())
+              << std::endl;
+    std::cout << sum(std::numeric_limits<float>::max(),
+                     std::numeric_limits<float>::max())
+              << std::endl;
+    std::cout << sum(std::numeric_limits<double>::max(),
+                     std::numeric_limits<double>::max())
+              << std::endl; // too large
+    std::cout << sum(std::numeric_limits<long double>::max(),
+                     std::numeric_limits<long double>::max())
+              << std::endl; // too large
+}