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README.adoc 

= Hello Headers

:toc:
:toc-placement!:

toc::[]


[[intro]]
Introduction
------------

Shows a hello world example which uses a different folder for source and include
files.

The files in this tutorial are below:

```
B-hello-headers$ tree
.
├── CMakeLists.txt
├── inc
│   └── Hello.h
└── src
    ├── Hello.cpp
    └── main.cpp
```

  * CMakeLists.txt - Contains the CMake commands you wish to run
  * inc/Hello.h - The header file to include
  * src/Hello.cpp - A source file to compile
  * src/main.cpp - The source file with main

[[concepts]]
Concepts
~~~~~~~~

[[directory-paths]]
Directory Paths
^^^^^^^^^^^^^^^

CMake syntax specifies a number of https://cmake.org/Wiki/CMake_Useful_Variables[variables]
which can be used to help find useful directories in your project or source tree.
Some of these include:

[cols=",",options="header",]
|=======================================================================
|Variable |Info
|CMAKE_SOURCE_DIR |The root source directory

|CMAKE_CURRENT_SOURCE_DIR |The current source directory if using
sub-projects and directories

|PROJECT_SOURCE_DIR |The source director of the current cmake project.

|CMAKE_BINARY_DIR |The root binary / build directory. This is the
directory you run the cmake command from

|CMAKE_CURRENT_BINARY_DIR |The build directory you are currently in.

|PROJECT_BINARY_DIR |The build directory for the current project.
|=======================================================================

[[including-directories]]
Including Directories
^^^^^^^^^^^^^^^^^^^^^

When you have different include folders, you can make your compiler aware of them using the
+include_directories()+ function. This will add these directories to the
compiler with the -I flag e.g. `-I/directory/path`

[source,cmake]
----
include_directories(
    ${PROJECT_SOURCE_DIR}/inc
    )
----



[[setting-source-files]]
Source Files Variable
^^^^^^^^^^^^^^^^^^^^

Creating a variable which includes the source files allows you to be
clearer about these files and easily add them to multiple commands, for example,
the +add_executable()+ function.

[source,cmake]
----
# Create a sources variable with a link to all cpp files to compile
set(SOURCES
    src/Hello.cpp
    src/main.cpp
)

add_executable(${PROJECT_NAME} ${SOURCES})
----

[NOTE]
====
An alternative to setting specific file names in the +SOURCES+ variable is
to use a GLOB command to find files using wildcard pattern matching.


[source,cmake]
----
file(GLOB SOURCES "src/*.cpp")
----
====

[[building-the-example]]
Building the Example
~~~~~~~~~~~~~~~~~~~~

[source,bash]
----
$ mkdir build

$ cd build

$ cmake ..
-- The C compiler identification is GNU 4.8.4
-- The CXX compiler identification is GNU 4.8.4
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Configuring done
-- Generating done
-- Build files have been written to: /home/matrim/workspace/cmake-examples/01-basic/hello_headers/build

$ make
Scanning dependencies of target hello_headers
[ 50%] Building CXX object CMakeFiles/hello_headers.dir/src/Hello.cpp.o
[100%] Building CXX object CMakeFiles/hello_headers.dir/src/main.cpp.o
Linking CXX executable hello_headers
[100%] Built target hello_headers

$ ./hello_headers
Hello Headers!
----

[[verbose-output]]
Verbose Output
^^^^^^^^^^^^^^

In the previous examples, when running the make command the output only
shows the status of the build. To see the full output for debugging
purposes you can add +VERBOSE=1+ flag when running make.

The VERBOSE output is show below, and a examination of the output shows
the include directories being added to the c++ compiler command.

[source,bash]
----
$ make clean

$ make VERBOSE=1
/usr/bin/cmake -H/home/matrim/workspace/cmake-examples/01-basic/hello_headers -B/home/matrim/workspace/cmake-examples/01-basic/hello_headers/build --check-build-system CMakeFiles/Makefile.cmake 0
/usr/bin/cmake -E cmake_progress_start /home/matrim/workspace/cmake-examples/01-basic/hello_headers/build/CMakeFiles /home/matrim/workspace/cmake-examples/01-basic/hello_headers/build/CMakeFiles/progress.marks
make -f CMakeFiles/Makefile2 all
make[1]: Entering directory `/home/matrim/workspace/cmake-examples/01-basic/hello_headers/build'
make -f CMakeFiles/hello_headers.dir/build.make CMakeFiles/hello_headers.dir/depend
make[2]: Entering directory `/home/matrim/workspace/cmake-examples/01-basic/hello_headers/build'
cd /home/matrim/workspace/cmake-examples/01-basic/hello_headers/build && /usr/bin/cmake -E cmake_depends "Unix Makefiles" /home/matrim/workspace/cmake-examples/01-basic/hello_headers /home/matrim/workspace/cmake-examples/01-basic/hello_headers /home/matrim/workspace/cmake-examples/01-basic/hello_headers/build /home/matrim/workspace/cmake-examples/01-basic/hello_headers/build /home/matrim/workspace/cmake-examples/01-basic/hello_headers/build/CMakeFiles/hello_headers.dir/DependInfo.cmake --color=
make[2]: Leaving directory `/home/matrim/workspace/cmake-examples/01-basic/hello_headers/build'
make -f CMakeFiles/hello_headers.dir/build.make CMakeFiles/hello_headers.dir/build
make[2]: Entering directory `/home/matrim/workspace/cmake-examples/01-basic/hello_headers/build'
/usr/bin/cmake -E cmake_progress_report /home/matrim/workspace/cmake-examples/01-basic/hello_headers/build/CMakeFiles 1
[ 50%] Building CXX object CMakeFiles/hello_headers.dir/src/Hello.cpp.o
/usr/bin/c++    -I/home/matrim/workspace/cmake-examples/01-basic/hello_headers/inc    -o CMakeFiles/hello_headers.dir/src/Hello.cpp.o -c /home/matrim/workspace/cmake-examples/01-basic/hello_headers/src/Hello.cpp
/usr/bin/cmake -E cmake_progress_report /home/matrim/workspace/cmake-examples/01-basic/hello_headers/build/CMakeFiles 2
[100%] Building CXX object CMakeFiles/hello_headers.dir/src/main.cpp.o
/usr/bin/c++    -I/home/matrim/workspace/cmake-examples/01-basic/hello_headers/inc    -o CMakeFiles/hello_headers.dir/src/main.cpp.o -c /home/matrim/workspace/cmake-examples/01-basic/hello_headers/src/main.cpp
Linking CXX executable hello_headers
/usr/bin/cmake -E cmake_link_script CMakeFiles/hello_headers.dir/link.txt --verbose=1
/usr/bin/c++       CMakeFiles/hello_headers.dir/src/Hello.cpp.o CMakeFiles/hello_headers.dir/src/main.cpp.o  -o hello_headers -rdynamic
make[2]: Leaving directory `/home/matrim/workspace/cmake-examples/01-basic/hello_headers/build'
/usr/bin/cmake -E cmake_progress_report /home/matrim/workspace/cmake-examples/01-basic/hello_headers/build/CMakeFiles  1 2
[100%] Built target hello_headers
make[1]: Leaving directory `/home/matrim/workspace/cmake-examples/01-basic/hello_headers/build'
/usr/bin/cmake -E cmake_progress_start /home/matrim/workspace/cmake-examples/01-basic/hello_headers/build/CMakeFiles 0
----