Updating to C++23

Author: cpp-tutor

headers/01-hellow.cpp

@@ -1,8 +1,8 @@
 // 01-hellow.cpp : prints a line of text to the console
 
-#include <iostream>
+#include <print>
 using namespace std;
 
 int main() {
-    cout << "Hello, World!" << '\n';
+    println("Hello, World!");
 }

headers/01-title.cpp

@@ -1,15 +1,15 @@
 // 01-title.cpp : output the title page of a well-known book
 
-#include <iostream>
+#include <print>
 using namespace std;
 
 int main() {
-    cout << 1+R"(
+    print(1+R"(
                    Alice's
                 Adventures In
                  Wonderland
 
                      by
                 LEWIS CARROLL
-)";
+)");
 }

headers/02-assign.cpp

@@ -1,14 +1,14 @@
 // 02-assign.cpp : assign to local variables
 
-#include <iostream>
+#include <print>
 using namespace std;
 
 int main() {
     int i = 1, j = 2;
     unsigned k;
-    cout << "(1) i = " << i << ", j = " << j << ", k = " << k << '\n';
+    println("(1) i = {}, j = {}, k = {}", i, j, k);
     i = j;
     j = 3;
     k = -1;
-    cout << "(2) i = " << i << ", j = " << j << ", k = " << k << '\n';
+    println("(2) i = {}, j = {}, k = {}", i, j, k);
 }

headers/02-constants.cpp

@@ -1,13 +1,12 @@
 // 02-constants.cpp : introducing the const keyword
 
-#include <iostream>
+#include <print>
 using namespace std;
 
 const double PI = 3.14159265358979;
 
 int main() {
     auto const APPROX_E = 3;
-    cout << "pi is almost exactly " << PI
-    << "e is approximately " << APPROX_E
-    << '\n';
+    println("pi is almost exactly {}, while e is approximately {}",
+        PI, APPROX_E);
 }

headers/02-constexpr.cpp

@@ -1,17 +1,16 @@
 // 02-constexpr.cpp : introducing the constexpr keyword
 
-#include <iostream>
+#include <print>
 #include <cmath>
 using namespace std;
 
-const double PI1 = acos(-1.0);     // acos is not (yet) constexpr
+constexpr double PI1 = acos(-1.0);
 constexpr double PI2 = 22.0 / 7.0;
 
-// the following line does not compile and has been commented out
-//static_assert(PI1 > 3.141 && PI1 < 3.143);
+static_assert(PI1 > 3.141 && PI1 < 3.143);
 static_assert(PI2 > 3.141 && PI2 < 3.143);
 
 int main() {
-    cout << "PI1 = " << PI1 << '\n';
-    cout << "PI2 = " << PI2 << '\n';
+    println("PI1 = {}", PI1);
+    println("PI2 = {}", PI2);
 }

headers/02-height.cpp

@@ -1,6 +1,6 @@
 // 02-height.cpp : define the same variable name in two different namespaces
 
-#include <iostream>
+#include <print>
 using namespace std;
 
 namespace Wonderland {
@@ -12,9 +12,7 @@ namespace VictorianEngland {
 }
 
 int main() {
-    cout << "Alice\'s height varies between "
-    << Wonderland::alice_height_m
-    << "m and "
-    << VictorianEngland::alice_height_m
-    << "m.\n";
+    println("Alice\'s height varies between {}m and {}m",
+        Wonderland::alice_height_m,
+        VictorianEngland::alice_height_m);
 }

headers/02-references.cpp

@@ -1,13 +1,13 @@
 // 02-references.cpp : introducing l-value references
 
-#include <iostream>
+#include <print>
 using namespace std;
 
 int alice_age{ 9 };
 
 int main() {
-    cout << "Alice\'s age is " << alice_age << '\n';
+    println("Alice\'s age is {}", alice_age);
     int& alice_age_ref = alice_age;
     alice_age_ref = 10;
-    cout << "Alice\'s age is now " << alice_age << '\n';
+    println("Alice\'s age is now {}", alice_age);
 }

headers/02-scopes.cpp

@@ -1,16 +1,16 @@
 // 02-scopes.cpp : define three variables with the same name in one program
 
-#include <iostream>
+#include <print>
 using namespace std;
 
 auto a{ 1.5f };
 
 int main() {
-    cout << "(1) " << a << '\n';
+    println("(1) {}", a);
     auto a{ 2u };
-    cout << "(2) " << a << '\n';
+    println("(2) {}", a);
     {
         auto a{ 2.5 };
-        cout << "(3) " << a << '\n';
+        println("(3) {}", a);
     }
 }

headers/02-swap.cpp

@@ -1,13 +1,13 @@
 // 02-swap.cpp : attempt to swap the values of an int and a double
 
-#include <iostream>
+#include <print>
 using namespace std;
 
 int main() {
     int a = 1;
     double b = 2.5;
-    cout << "(1) a = " << a << ", b = " << b << '\n';
+    println("(1) a = {}, b = {}", a, b);
     a = 2.5;
     b = 1;
-    cout << "(2) a = " << a << ", b = " << b << '\n';
+    println("(2) a = {}, b = {}", a, b);
 }

headers/02-uniform.cpp

@@ -1,11 +1,11 @@
 // 02-uniform.cpp : avoid compiler error with uniform initialization and explicit narrowing cast
 
-#include <iostream>
+#include <print>
 using namespace std;
 
 int main() {
     // int c = { 2.5 };                 // Error: this does NOT compile
     int c = { static_cast<int>(2.5) };  // while this does
     double d = { 1 };                   // and so does this
-    cout << "c = " << c << ", d = " << d << '\n';
+    println("c = {}, d = {}", c, d);
 }

headers/03-calc.cpp

@@ -6,7 +6,7 @@ using namespace std;
 int main() {
     int r{}, x{}, y{};
     char op{};
-    cout << "Please enter a calulation (number op number, op is one of +-*/):\n";
+    cout << "Please enter a calculation (number op number, op is one of +-*/):\n";
     cin >> x >> op >> y;
     switch (op) {
     case '+':

headers/04-inline.cpp

@@ -1,6 +1,6 @@
 // 04-inline.cpp : use of an inline function
 
-#include <iostream>
+#include <print>
 using namespace std;
 
 inline void swap(int& x, int& y) {
@@ -11,7 +11,7 @@ inline void swap(int& x, int& y) {
 
 int main() {
     int a = 1, b = 2;
-    cout << "(1) a = " << a << ", b = " << b << '\n';
+    println("(1) a = {}, b = {}", a, b);
     swap(a, b);
-    cout << "(2) a = " << a << ", b = " << b << '\n';
+    println("(2) a = {}, b = {}", a, b);
 }

headers/04-noexcept.cpp

@@ -1,14 +1,14 @@
 // 04-noexcept.cpp : a noexcept function throwing an exception
 
-#include <iostream>
+#include <print>
 #include <stdexcept>
 using namespace std;
 
 int throw_if_zero(int i) noexcept {
     if (!i) {
         throw runtime_error("found a zero");
     }
-    cout << "throw_if_zero(): " << i << '\n';
+    println("throw_if_zero(): {}", i);
 }
 
 int main() {
@@ -18,7 +18,7 @@ int main() {
         throw_if_zero(0);
     }
     catch(...) {
-        cout << "Caught an exception!\n";
+        println("Caught an exception!");
     }
-    cout << "Leaving main()\n";
+    println("Leaving main()\n");
 }

headers/04-static-var.cpp

@@ -1,11 +1,11 @@
 // 04-static-var.cpp : preserving function state in a static variable
 
-#include <iostream>
+#include <print>
 using namespace std;
 
 void f() {
     static int s{1};
-    cout << s << '\n';
+    println("{}", s);
     ++s;
 }
 

headers/06-pixel1.cpp

@@ -19,15 +19,13 @@ string_view get_color(Color c) {
     switch (c) {
         case Color::red:
             return "red";
-            break;
         case Color::green:
             return "green";
-            break;
         case Color::blue:
             return "blue";
-            break;
+        default:
+            return "<no color>";
     }
-    return "<no color>";
 }
 
 int main() {

headers/06-pixel2.cpp

@@ -18,15 +18,13 @@ string_view get_color(Color c) {
     switch (c) {
         case Color::red:
             return "red";
-            break;
         case Color::green:
             return "green";
-            break;
         case Color::blue:
             return "blue";
-            break;
+        default:
+            return "<no color>";
     }
-    return "<no color>";
 }
 
 int main() {

headers/06-point3.cpp

@@ -7,7 +7,7 @@ struct Point{
     int x{}, y{};
 };
 
-Point operator+ (const Point& lhs, const Point& rhs) {
+const Point operator+ (const Point& lhs, const Point& rhs) {
     Point result;
     result.x = lhs.x + rhs.x;
     result.y = lhs.y + rhs.y;

headers/06-point4.cpp

@@ -13,7 +13,7 @@ struct Point{
     }
 };
 
-Point operator+ (const Point& lhs, const Point& rhs) { // non-member operator+
+const Point operator+ (const Point& lhs, const Point& rhs) { // non-member operator+
     Point result{ lhs };
     result += rhs;
     return result;

headers/08-format1.cpp

@@ -0,0 +1,12 @@
+// 08-format1.cpp : Basic usage of format string
+
+#include <print>
+#include <string>
+using namespace std;
+
+int main() {
+    string s{ "Formatted" };
+    auto d{ 10.0 / 3.0 };
+    auto i{ 20000 };
+    println("{0:20}:{2:8}, {1:12.11}", s, d, i);
+}

headers/08-format2.cpp

@@ -0,0 +1,31 @@
+// 08-format2.cpp : Various format string-using functions
+
+#include <print>
+#include <format>
+#include <string>
+#include <iostream>
+#include <iterator>
+#include <array>
+#include <cmath>
+using namespace std;
+
+int main() {
+    string world{ "World" };
+    print(cout, "Hello, {}!\n", world);
+    println("{1} or {0}", false, true);
+    
+    constexpr const char *fmt = "Approximation of π = {:.12g}";
+    string s = format(fmt, asin(1.0) * 2);
+    cout << s << '\n';
+    
+    constexpr const wchar_t *wfmt = L"Approximation of pi = {:.12g}";
+    wstring ws = format(wfmt, asin(1.0) * 2);
+    wcout << ws << L'\n';
+    
+    format_to(ostream_iterator<char>(cout), "Hello, {}!\n", world);
+    wstring ww{ L"World" };
+    array<wchar_t,9> wa;
+    auto iter = format_to_n(wa.begin(), 8, L"Hello, {}!\n", ww);
+    *(iter.out) = L'\0';
+    wcout << wa.data() << L'\n';
+}

headers/09-person1.cpp

@@ -1,27 +1,26 @@
 // 09-person1.cpp : model Person as a class with constructor
 
+#include <chrono>
 #include <iostream>
 #include <string>
 #include <string_view>
 using namespace std;
-
-struct Date {
-    int year{}, month{}, day{};
-};
+using namespace std::chrono;
 
 class Person {
 public:
-    Person(const Date& dob, string_view familyname, string_view firstname)
+    Person(const year_month_day& dob, string_view familyname, string_view firstname)
         : dob{ dob }, familyname{ familyname }, firstname{ firstname }
         {}
     string getName() const { return firstname + ' ' + familyname; }
+    const year_month_day& getDob() const { return dob; }
 private:
-    const Date dob;
+    const year_month_day dob;
     string familyname, firstname;
 };
 
 
 int main() {
-    Person genius{ { 1879, 3, 14 }, "Einstein", "Albert" };
-    cout << genius.getName() << '\n';
+    Person genius{ { 1879y, March, 14d }, "Einstein", "Albert" };
+    cout << genius.getName() << " was born " << genius.getDob() << '\n';
 }