Adjust to compilation as CMake sub-directory

**NOTE:** This change breaks backward compatibility, by changing the
CMake configuration options.

Avoid possible option collisions when using pfs as sub-directory.
Some options are supposed to be inherited from the project and are common
CMake flags, like the `CMAKE_BUILD_TYPE` or `BUILD_SHARED_LIBS`.
Whereas other flags are not supposed to be shared, and hence should are
to be prefixed with the project name.

Using `pfs_` for the prefix, rather than `PFS_` because CMake
automatically generates some library specific variables (Check that out
by looking at `CMakeCache.txt`) and uses the project name (`pfs`) as the
prefix.
This choice has been also observed in protobuf's CMake code.

CMakeLists.txt

@@ -1,16 +1,34 @@
 cmake_minimum_required (VERSION 3.5)
 
-project(pfs)
+project (pfs)
 
-option(BUILD_SHARED_LIBS "Build shared library (.so) instead of static one (.a)" ON)
-option(ADDRESS_SANITIZER "Enable address sanitizer" OFF)
-option(BUILD_SAMPLES "Build samples" ON)
-option(BUILD_TESTS "Build tests" ON)
+# ------------------------------------------------------------------------
+# Flags that are expected to be shared when added as sub-directory
+# ------------------------------------------------------------------------
+
+option (pfs_BUILD_SHARED_LIBS "Build a shared library instead of static one" ${BUILD_SHARED_LIBS})
+if (pfs_BUILD_SHARED_LIBS)
+    set (pfs_SHARED_OR_STATIC "SHARED")
+else ()
+    set (pfs_SHARED_OR_STATIC "STATIC")
+endif ()
 
 if (NOT CMAKE_BUILD_TYPE)
+    message (STATUS "Build type not specified. Set by default to DEBUG!")
     set (CMAKE_BUILD_TYPE Debug)
 endif ()
-message(STATUS "Build type: ${CMAKE_BUILD_TYPE}")
+
+# ------------------------------------------------------------------------
+# Flags that are NOT expected to be shared when added as sub-directory
+# ------------------------------------------------------------------------
+
+option (pfs_BUILD_ASAN "Enable address sanitizer" OFF)
+option (pfs_BUILD_SAMPLES "Build samples" ON)
+option (pfs_BUILD_TESTS "Build tests" ON)
+
+# ------------------------------------------------------------------------
+# Actual configuration
+# ------------------------------------------------------------------------
 
 add_compile_options (-std=c++11 -Wall -Wextra -pedantic -Werror)
 
@@ -20,29 +38,28 @@ set (CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/out)
 set (CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib)
 set (CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib)
 
-set (ROOT_SOURCE_DIR src)
-aux_source_directory (${ROOT_SOURCE_DIR} ROOT_SOURCES)
-aux_source_directory (${ROOT_SOURCE_DIR}/parsers PARSERS_SOURCES)
-set (SOURCES ${ROOT_SOURCES} ${PARSERS_SOURCES})
+set (pfs_ROOT_SOURCE_DIR src)
+aux_source_directory (${pfs_ROOT_SOURCE_DIR} pfs_ROOT_SOURCES)
+aux_source_directory (${pfs_ROOT_SOURCE_DIR}/parsers pfs_PARSERS_SOURCES)
+set (SOURCES ${pfs_ROOT_SOURCES} ${pfs_PARSERS_SOURCES})
 
-add_library (pfs ${SOURCES})
+add_library (pfs ${pfs_SHARED_OR_STATIC} ${SOURCES})
 
-if (ADDRESS_SANITIZER MATCHES ON)
-    message (STATUS "Enabling address sanitizer")
-    set (SANITIZE_FLAGS -fno-omit-frame-pointer -fsanitize=address -fsanitize=leak)
-    target_compile_options (pfs PUBLIC ${SANITIZE_FLAGS})
-    target_link_libraries (pfs PUBLIC -lasan ${SANITIZE_FLAGS})
+if (pfs_BUILD_ASAN)
+    set (pfs_BUILD_ASAN_FLAGS -fno-omit-frame-pointer -fsanitize=address -fsanitize=leak)
+    target_compile_options (pfs PUBLIC ${pfs_BUILD_ASAN_FLAGS})
+    target_link_libraries (pfs PUBLIC -lasan ${pfs_BUILD_ASAN_FLAGS})
 endif ()
 
-if (BUILD_SAMPLES)
-    aux_source_directory (sample SAMPLE_SOURCES)
-    add_executable (sample ${SAMPLE_SOURCES})
+if (pfs_BUILD_SAMPLES)
+    aux_source_directory (sample pfs_SAMPLE_SOURCES)
+    add_executable (sample ${pfs_SAMPLE_SOURCES})
     target_link_libraries (sample PRIVATE pfs)
 endif()
 
-if (BUILD_TESTS)
-    set (UNITTEST_SOURCE_DIR test)
-    aux_source_directory (${UNITTEST_SOURCE_DIR} UNITTEST_SOURCES)
-    add_executable (unittest ${UNITTEST_SOURCES})
+if (pfs_BUILD_TESTS)
+    set (pfs_UNITTEST_SOURCE_DIR test)
+    aux_source_directory (${pfs_UNITTEST_SOURCE_DIR} pfs_UNITTEST_SOURCES)
+    add_executable (unittest ${pfs_UNITTEST_SOURCES})
     target_link_libraries (unittest PRIVATE pfs)
 endif()

README.md

@@ -8,16 +8,18 @@ Very easy to use, procfs parsing library in C++.
 
 Run `cmake . && make`
 
-Currently supported CMake configuration flags:
+### Currently supported CMake configuration flags:
 
 - `CMAKE_BUILD_TYPE=<Debug|Release>`: Standard CMake flags to control build type (DEFAULT: Debug)
-- `BUILD_SHARED_LIBS=<ON|OFF>`: ON to compile a shared library. OFF to compile a static library (DEFAULT: ON)
-- `ENABLE_SANITIZER=<ON|OFF>`: ON to enable address sanitizer
-- `BUILD_SAMPLES=<ON|OFF>`: ON to build the sample programs
-- `BUILD_TESTS=<ON|OFF>`: ON to build the tests
+- `pfs_BUILD_SHARED_LIBS=<ON|OFF>`: ON to compile a shared library. OFF to compile a static library (DEFAULT: Inherit `BUILD_SHARE_LIBS`, which is `OFF` by default))
+- `pfs_BUILD_ASAN=<ON|OFF>`: ON to enable address sanitizer (DEFAULT: `OFF`)
+- `pfs_BUILD_SAMPLES=<ON|OFF>`: ON to build the sample programs (DEFAULT: `ON`)
+- `pfs_BUILD_TESTS=<ON|OFF>`: ON to build the tests (DEFAULT: `ON`)
 
 You can pass any number of those to the `cmake` command: `cmake -D<CONFIG_FLAG>=<VALUE> .`
 
+**NOTE**: After running `cmake` for the first time, some values are cached in `CMakeCache.txt` and will not change when running `cmake` for a second time with different flags.
+
 ### Build using clang
 
 If you prefer using clang, just configure the compiler while running cmake: