Exercises: Add interceptor library

exercises/README.md

@@ -329,3 +329,31 @@ Explain all parts like it's done in the lecture.
 
 Take a look at [Boost Operators](https://www.boost.org/doc/libs/1_74_0/libs/utility/operators.htm).
 Try to understand *why* the *curiously recurring template pattern (CRTP)* is used.
+
+## Task 22
+
+You are given the code and build instructions for a shared library and an executable which uses the shared library.
+The shared library features two functions `random_number` and `just_a_print` inside the `foo` namespace.
+
+Your task is to create an *interceptor* library:
+
+- `random_number` should be replaced with a function that always returns `4` for improved determinism
+- `just_a_print` should be wrapped so that some text is printed before and after the original function is executed
+
+Running the executable with and without the interceptor library could look like this:
+
+```
+$ ./executable
+Random Number: 880806932
+
+Just a print to stdout, nothing else
+
+$ LD_PRELOAD=$PWD/interceptor.so ./executable
+Random Number: 4
+
+some text before
+Just a print to stdout, nothing else
+some text after
+```
+
+**Hint:** For Linux, have a look at the related man-pages, like *ld-linux(8)*.

exercises/task22/CMakeLists.txt

@@ -0,0 +1,12 @@
+cmake_minimum_required(VERSION 3.8)
+project(example LANGUAGES CXX)
+
+set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+set(CMAKE_CXX_EXTENSIONS OFF)
+
+add_library(foo SHARED libFoo/foo.cpp)
+target_include_directories(foo PUBLIC libFoo)
+
+add_executable(executable executable.cpp)
+target_link_libraries(executable foo)

exercises/task22/executable.cpp

@@ -0,0 +1,9 @@
+#include <iostream>
+
+#include "foo.hpp"
+
+int main()
+{
+	std::cout << "Random Number: " << foo::random_number() << "\n\n";
+	foo::just_a_print();
+}

exercises/task22/libFoo/foo.cpp

@@ -0,0 +1,23 @@
+#include "foo.hpp"
+
+#include <iostream>
+#include <limits>
+#include <random>
+
+namespace foo {
+
+int random_number()
+{
+	static std::random_device device;
+	static std::mt19937 rng(device());
+	static std::uniform_int_distribution<int> dist(0, std::numeric_limits<int>::max());
+
+	return dist(rng);
+}
+
+void just_a_print()
+{
+	std::cout << "Just a print to stdout, nothing else\n";
+}
+
+} // end namespace foo

exercises/task22/libFoo/foo.hpp

@@ -0,0 +1,12 @@
+#ifndef FOO_HPP
+#define FOO_HPP
+
+namespace foo {
+
+int random_number();
+
+void just_a_print();
+
+} // end namespace foo
+
+#endif // FOO_HPP