CMake

It is often helpful to include the current directory for C++ projects. When using GCC directly, this can be done using -I., whereas for CMake you need to use the following statement:

target_include_directories(myexe PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})

Remember to replace myexe by the name of your executable target.

Problem:

You are trying to build your CMake-based project using a CMakeLists.txt like

cmake_minimum_required(VERSION 3.10)
project(my_project)

add_executable(my_project *.cpp)

Solution:

You can’t use the glob pattern *.cpp directly in add_executable(). You need to use file(GLOB ...) in order to set a variable, which you can then use in add_executable():

cmake_minimum_required(VERSION 3.10)
project(my_project)

file(GLOB SRC_FILES *.cpp)
add_executable(my_project ${SRC_FILES})

Problem:

In your CMakeLists.txt, you want to add an include directory such as /usr/include/mylibrary for the executable myexe using code like:

target_include_directories( myexe /usr/include/mylib )

But when you try to configure the build using cmake . or make, you see an error message like

CMake Error at CMakeLists.txt:8 (target_include_directories):
  target_include_directories called with invalid arguments


-- Configuring incomplete, errors occurred!

Solution:

You need to add PUBLIC between the target name (myexe) and the include directory/directories:

target_include_directories( myexe PUBLIC /usr/include/mylib )

This CMakeLists.txt builds an executable called main from main.cpp:

add_executable(main main.cpp)

With automake/m4 in configure.ac you use syntax like

AC_CHECK_FUNCS(atan2)

which defines HAVE_FDATASYNC if the function is available.

In CMake, you can use check_symbol_exists() for the same purpose like this:

cmake_minimum_required(VERSION 3.0)
include(CheckSymbolExists)

# Define executable
add_executable(myexe main.c)

# atan2 requires the math library to be linked
list(APPEND CMAKE_REQUIRED_LIBRARIES m)
check_symbol_exists(atan2 math.h HAVE_ATAN2)

# Add compile definitions if we have the library
if(HAVE_ATAN2)
    target_compile_definitions(myexe PRIVATE -DHAVE_ATAN2)
endif()

Note that check_symbol_exists() does not automatically add a preprocessor define but you have to do that manually (see the last block in the code shown above). While this might seem less comfortable at first, this approach provides you with much more flexibility on how to handle missing or available functions.

See the CMake check_symbol_exists() documentation for more details.

cmake_minimum_required(VERSION 3.0)
include(CheckSymbolExists)

# Define executable
add_executable(myexe main.c)

# atan2 requires the math library to be linked
list(APPEND CMAKE_REQUIRED_LIBRARIES m)
check_symbol_exists(atan2 math.h HAVE_ATAN2)

# Add compile definitions if we have the library
if(HAVE_ATAN2)
    target_compile_definitions(myexe PRIVATE -DHAVE_ATAN2)
endif()

If you have CMake code using check_symbol_exists(...) like

list(APPEND CMAKE_REQUIRED_LIBRARIES m)
check_symbol_exists(atan2 math.h HAVE_ATAN2)

but you get an error message like

CMake Error at CMakeLists.txt:8 (check_symbol_exists):
  Unknown CMake command "check_symbol_exists".

-- Configuring incomplete, errors occurred!

you need to add

include(CheckSymbolExists)

near the top of your CMakeLists.txt (before your first call to check_symbol_exists()).

if/else/endif looks like this in CMake:

if(myvar)
  message("if")
else()
  message("else")
endif()

Problem:

You are trying to build a software that is using the CMake build system.

You are trying to run make to build, but you see this error message:

make: *** No targets specified and no makefile found.  Stop.

Solution:

Before running make, you need to configure your build using CMake.

The simplest way of doing that is to run

cmake .

Typically you only need to do that once for each project ; CMake will automatically detect changes to CMakeLists.txt when you run make.

After that, you can run make again. If the build is successful, you’ll see a message like this:

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