Started a cmake tutorial

Step4/CMakeLists.txt

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+# TODO 1: Update the minimum required version to 3.15
+
+cmake_minimum_required(VERSION 3.10)
+
+# set the project name and version
+project(Tutorial VERSION 1.0)
+
+# specify the C++ standard
+add_library(tutorial_compiler_flags INTERFACE)
+target_compile_features(tutorial_compiler_flags INTERFACE cxx_std_11)
+
+# TODO 2: Create helper variables to determine which compiler we are using:
+# * Create a new variable gcc_like_cxx that is true if we are using CXX and
+#   any of the following compilers: ARMClang, AppleClang, Clang, GNU, LCC
+# * Create a new variable msvc_cxx that is true if we are using CXX and MSVC
+# Hint: Use set() and COMPILE_LANG_AND_ID
+
+# TODO 3: Add warning flag compile options to the interface library
+# tutorial_compiler_flags.
+# * For gcc_like_cxx, add flags -Wall;-Wextra;-Wshadow;-Wformat=2;-Wunused
+# * For msvc_cxx, add flags -W3
+# Hint: Use target_compile_options()
+
+# TODO 4: With nested generator expressions, only use the flags for the
+# build-tree
+# Hint: Use BUILD_INTERFACE
+
+# configure a header file to pass some of the CMake settings
+# to the source code
+configure_file(TutorialConfig.h.in TutorialConfig.h)
+
+# add the MathFunctions library
+add_subdirectory(MathFunctions)
+
+# add the executable
+add_executable(Tutorial tutorial.cxx)
+
+target_link_libraries(Tutorial PUBLIC MathFunctions tutorial_compiler_flags)
+
+# add the binary tree to the search path for include files
+# so that we will find TutorialConfig.h
+target_include_directories(Tutorial PUBLIC
+                           "${PROJECT_BINARY_DIR}"
+                           )

Step4/MathFunctions/CMakeLists.txt

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+# create the MathFunctions library
+add_library(MathFunctions MathFunctions.cxx)
+
+# state that anybody linking to us needs to include the current source dir
+# to find MathFunctions.h, while we don't.
+target_include_directories(MathFunctions
+                           INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}
+                           )
+
+# should we use our own math functions
+option(USE_MYMATH "Use tutorial provided math implementation" ON)
+if (USE_MYMATH)
+  target_compile_definitions(MathFunctions PRIVATE "USE_MYMATH")
+
+  # library that just does sqrt
+  add_library(SqrtLibrary STATIC
+              mysqrt.cxx
+              )
+
+  # link SqrtLibrary to tutorial_compiler_flags
+  target_link_libraries(SqrtLibrary PUBLIC tutorial_compiler_flags)
+
+  target_link_libraries(MathFunctions PRIVATE SqrtLibrary)
+endif()
+
+# link MathFunctions to tutorial_compiler_flags
+target_link_libraries(MathFunctions PUBLIC tutorial_compiler_flags)

Step4/MathFunctions/MathFunctions.cxx

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+#include "MathFunctions.h"
+
+#include <cmath>
+
+#ifdef USE_MYMATH
+#  include "mysqrt.h"
+#endif
+
+namespace mathfunctions {
+double sqrt(double x)
+{
+// which square root function should we use?
+#ifdef USE_MYMATH
+  return detail::mysqrt(x);
+#else
+  return std::sqrt(x);
+#endif
+}
+}

Step4/MathFunctions/MathFunctions.h

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+#pragma once
+
+namespace mathfunctions {
+double sqrt(double x);
+}

Step4/MathFunctions/mysqrt.cxx

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+#include "mysqrt.h"
+
+#include <iostream>
+
+namespace mathfunctions {
+namespace detail {
+// a hack square root calculation using simple operations
+double mysqrt(double x)
+{
+  if (x <= 0) {
+    return 0;
+  }
+
+  double result = x;
+
+  // do ten iterations
+  for (int i = 0; i < 10; ++i) {
+    if (result <= 0) {
+      result = 0.1;
+    }
+    double delta = x - (result * result);
+    result = result + 0.5 * delta / result;
+    std::cout << "Computing sqrt of " << x << " to be " << result << std::endl;
+  }
+  return result;
+}
+}
+}

Step4/MathFunctions/mysqrt.h

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+#pragma once
+
+namespace mathfunctions {
+namespace detail {
+double mysqrt(double x);
+}
+}

Step4/TutorialConfig.h.in

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+// the configured options and settings for Tutorial
+#define Tutorial_VERSION_MAJOR @Tutorial_VERSION_MAJOR@
+#define Tutorial_VERSION_MINOR @Tutorial_VERSION_MINOR@

Step4/tutorial.cxx

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+// A simple program that computes the square root of a number
+#include <cmath>
+#include <iostream>
+#include <string>
+
+#include "MathFunctions.h"
+#include "TutorialConfig.h"
+
+int main(int argc, char* argv[])
+{
+  if (argc < 2) {
+    // report version
+    std::cout << argv[0] << " Version " << Tutorial_VERSION_MAJOR << "."
+              << Tutorial_VERSION_MINOR << std::endl;
+    std::cout << "Usage: " << argv[0] << " number" << std::endl;
+    return 1;
+  }
+
+  // convert input to double
+  const double inputValue = std::stod(argv[1]);
+
+  const double outputValue = mathfunctions::sqrt(inputValue);
+
+  std::cout << "The square root of " << inputValue << " is " << outputValue
+            << std::endl;
+  return 0;
+}