C++, Debug/Release, CMake “Programming”, Rants

Source

09-c++/
├── CMakeLists.txt
├── bin
│   ├── CMakeLists.txt
│   ├── hello-first.cpp
│   └── hello-second.cpp
└── libhello
    ├── CMakeLists.txt
    ├── greeter.h
    ├── greeter-name.h
    ├── greeter-name.cpp
    ├── greeter-simple.h
    └── greeter-simple.cpp

• 09-c++/CMakeLists.txt

• 09-c++/bin/CMakeLists.txt

• 09-c++/bin/hello-first.cpp

• 09-c++/bin/hello-second.cpp

• 09-c++/libhello/CMakeLists.txt

• 09-c++/libhello/greeter.h

• 09-c++/libhello/greeter-simple.h

• 09-c++/libhello/greeter-simple.cpp

• 09-c++/libhello/greeter-name.h

• 09-c++/libhello/greeter-name.cpp

Pause

• Give trainer time to switch project to C++

Class Diagram

C++ Standard Version

Documentation

• cmake_cxx_standard

set(CMAKE_CXX_STANDARD 23)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

$ make VERBOSE=1
... /usr/bin/c++ -std=gnu++23 ...

Debug Vs. Release Builds: CMAKE_BUILD_TYPE

Documentation

• CMAKE_BUILD_TYPE

• Debug

  $ cmake -DCMAKE_BUILD_TYPE=Debug /home/jfasch/work/jfasch-home/trainings/material/soup/cmake/09-c++/
  $ make VERBOSE=1
  ... /usr/bin/c++ -O3 -DNDEBUG ...
  

  (Looks pretty arbitrary and half-hearted)

• Release

  $ cmake -DCMAKE_BUILD_TYPE=Release /home/jfasch/work/jfasch-home/trainings/material/soup/cmake/09-c++/
  $ make VERBOSE=1
  ... /usr/bin/c++ -O3 -DNDEBUG ...
  

  (Looks pretty arbitrary and half-hearted)

Compiler Type

Documentation

• CMAKE_<LANG>_COMPILER_ID

• if (and conditionals)

• Compiler flags chosen half-heartely by CMake

• ⟶ custom flags needed

• E.g. for “Debug”, but only if GCC

  • Optimization off (-O0), to improve single-stepping experience

  • Better debug info (-g3)

  • More warnings (-Wall) for sanity

  • Turn warnings into errors (-Werror) for sanity

if (${CMAKE_BUILD_TYPE} STREQUAL Debug)
  if (${CMAKE_C_COMPILER_ID} STREQUAL GNU)
    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -O0 -g3 -Wall -Werror")
  endif()
  if (${CMAKE_CXX_COMPILER_ID} STREQUAL GNU)
    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -O0 -g3 -Wall -Werror")
  endif()
endif()

Strings And Lists

Documentation

• string()

• list()

• CMake’s “language” has no type system

• Strings can be compared numerically or lexically ⟶ no errors, just bugs

• Lists are strings that contain semicolon separated values

• ⟶ CMake commands to manipulate strings and lists

if (${CMAKE_BUILD_TYPE} STREQUAL Debug)
  message(DEBUG "Oida! Debug Build!!")
  if (${CMAKE_C_COMPILER_ID} STREQUAL GNU)
    string(APPEND CMAKE_C_FLAGS "-O0 -g3 -Wall -Werror")
  endif()
  if (${CMAKE_CXX_COMPILER_ID} STREQUAL GNU)
    string(APPEND CMAKE_CXX_FLAGS "-O0 -g3 -Wall -Werror")
  endif()
endif()

• Show message() usage …

$ cmake --log-level=Debug  -DCMAKE_BUILD_TYPE=Debug /home/jfasch/work/jfasch-home/trainings/material/soup/cmake/09-c++/
-- Oida! Debug Build!!
...

message() (A.k.a printf() Debugging)

Documentation

• message()

• Basic usage

  message("Howdy")
  

  is the same as

  message(NOTICE "Howdy")
  

  is the same as

  message(Howdy)          # <--- root of all evil (one of roots)
  

⟶ all sorts of … crap:

• Tags? Enums? No!

  message(WARNING "Howdy")
  

  Prints, as expected …

  CMake Warning at CMakeLists.txt:5 (MESSAGE):
    Howdy
  

  message(BULLSHIT "Howdy")
  

  Prints …

  $ cmake ~/work/jfasch-home/trainings/material/soup/cmake/code/
  BULLSHITHowdy
  

message(): Popular “Modes”

Mode	Description
FATAL_ERROR	CMake Error, stop processing and generation.
SEND_ERROR	CMake Error, continue processing, but skip generation.
WARNING	CMake Warning, continue processing.
(none) or NOTICE	Important message printed to stderr to attract user’s attention.
STATUS	The main interesting messages that project users might be interested in. Ideally these should be concise, no more than a single line, but still informative.
VERBOSE	Detailed informational messages intended for project users. These messages should provide additional details that won’t be of interest in most cases, but which may be useful to those building the project when they want deeper insight into what’s happening.
DEBUG	Detailed informational messages intended for developers working on the project itself as opposed to users who just want to build it. These messages will not typically be of interest to other users building the project and will often be closely related to internal implementation details.
TRACE	Fine-grained messages with very low-level implementation details. Messages using this log level would normally only be temporary and would expect to be removed before releasing the project, packaging up the files, etc.

$ cmake --help
...
--log-level=<ERROR|WARNING|NOTICE|STATUS|VERBOSE|DEBUG|TRACE>
...

Attention

All of this lacks a clear definition. Apparently …

• Ordering appears to be ERROR > WARNING > NOTICE > STATUS > VERBOSE > DEBUG > TRACE

• STATUS is the default level