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helloworld

Hello World

Explainy Bits...

The source code is in main.cpp. But this isn't executable (runnable) until it gets compiled into an executable.

CMake is the tool we'll use to create an executable from our C++ source code.

The CMakeLists.txt file

The CMakeLists.txt file should contain a few simple commands. Based on those commands, a full make build environment is created.

cmake_minimum_required(VERSION 3.3)
project(HelloWorld)

add_executable(hello_world main.cpp)

The build directory

If the build directory doesn't exist, create it:

$ mkdir build

Once the build directory exists, move to that directory and run cmake ... This creates the make environment.

$ cd build
$ cmake ..

CMake Deprecation Warning at CMakeLists.txt:1 (cmake_minimum_required):
  Compatibility with CMake < 3.5 will be removed from a future version of
  CMake.

  Update the VERSION argument <min> value or use a ...<max> suffix to tell
  CMake that the project does not need compatibility with older versions.


-- The C compiler identification is AppleClang 15.0.0.15000309
-- The CXX compiler identification is AppleClang 15.0.0.15000309
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /Library/Developer/CommandLineTools/usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /Library/Developer/CommandLineTools/usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done (2.6s)
-- Generating done (0.0s)
-- Build files have been written to: /Users/scott/code/local/helloworld/build

The make build environment

CMake has now created a make build environment.

$ ls -al                            (main)helloworld
total 56
drwxr-xr-x   6 scott  staff    192 Oct 15 13:24 .
drwxr-xr-x  10 scott  staff    320 Oct 15 13:15 ..
-rw-r--r--   1 scott  staff  14202 Oct 15 13:24 CMakeCache.txt
drwxr-xr-x  13 scott  staff    416 Oct 15 13:24 CMakeFiles
-rw-r--r--   1 scott  staff   5331 Oct 15 13:24 Makefile
-rw-r--r--   1 scott  staff   1852 Oct 15 13:24 cmake_install.cmake

Specifically, the Makefile has all of the interesting stuff in it.

Making the executable

Finally, we are ready to make an executable from our source code. Type make to build the executable.

$ make                          (main)

helloworld
[ 50%] Building CXX object CMakeFiles/hello_world.dir/main.cpp.o
[100%] Linking CXX executable hello_world
[100%] Built target hello_world

Running the executable

Our executable is called hello_world. To run it, type ./hello_world.

$ ./hello_world

Hello World!