Build doxygen from CMake script

Question

I found on the Web a sample cmake file and put it in the /doc subdirectory of my project, where the file myproject.doxgen is also located, containi

Answer 1

The way the CMake file you've shown is set up, it creates a target called doc; building that target (such as running make doc) generates the doxymentation. The target is not part of make all (or equivalent); to make it such, add ALL into the custom target creation:

add_custom_target(
  doc ALL
  COMMAND #... everything else as before
)

If you want to limit this target to only build in a particular configuration (as you've mentioned in comments), you can use generator expressions:

add_custom_target(
  doc ALL
  COMMAND $<$<CONFIG:Release>:${DOXYGEN_EXECUTABLE} ${doxyfile_in}>
  WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/doc
  COMMENT "Generating API documentation with Doxygen"
  VERBATIM
)

It might happen that some CMake generators do not cope well with an empty COMMAND. With this in mind, the following should be fail-safe:

add_custom_target(
  doc ALL
  COMMAND
    $<$<CONFIG:Release>:${DOXYGEN_EXECUTABLE} ${doxyfile_in}>
    $<$<NOT:$<CONFIG:Release>>:${CMAKE_COMMAND} -E echo "Only done in Release builds">
  WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/doc
  COMMENT "Generating API documentation with Doxygen"
  VERBATIM
)