Question
Answer and Explanation
In CMakeLists.txt, there isn't a direct way to comment out part of a line using a specific inline comment syntax, like you might find in other languages. CMake uses the '#' character to denote a full-line comment, which means everything from the '#' character to the end of that line will be treated as a comment. However, there are some effective workarounds to achieve a similar effect if you wish to disable part of a line conditionally.
Here are the common methods you might consider:
1. Full-Line Commenting:
- The standard approach is to comment out the entire line using '#'. If you want to "disable" part of a line, but need to keep the rest, the typical way is splitting the line to two lines, and then comment out the unnecessary line.
Example:
# This is a fully commented line.
set(MY_VARIABLE "some value") #commented out text, but that is part of the string
#set(MY_VARIABLE "some value but commented out") # this line is commented out completely
2. Conditional Statements:
- For conditional disabling of parts of a line, you can use `if` statements. This can simulate conditional commenting during the CMake configuration process based on specific variables or properties.
Example:
set(USE_DEBUG_FLAG OFF)
if(USE_DEBUG_FLAG)
add_definitions(-DDEBUG) # This definition is included only if USE_DEBUG_FLAG is ON
endif()
add_executable(my_program main.cpp)
3. String Concatenation and Variable Substitution:
- In some cases, you can use string concatenation and variables to conditionally build parts of a command. This technique is helpful when you are modifying flags or arguments depending on certain conditions.
Example:
set(EXTRA_LINK_FLAGS "")
if(SOME_CONDITION)
set(EXTRA_LINK_FLAGS "-L/path/to/some/lib")
endif()
target_link_libraries(my_program ${EXTRA_LINK_FLAGS} some_lib)
4. Using Variables and String Operations:
- You can prepare the argument for a function in a separate variable, then conditionally modify that variable before using it in a function call.
Example:
set(COMPILE_FLAGS "-Wall")
if(SOME_CONDITION)
string(APPEND COMPILE_FLAGS " -O3")
endif()
add_compile_options(${COMPILE_FLAGS})
Important Considerations:
- CMake syntax emphasizes clear, readable logic, and avoiding complex inline conditional comments maintains the readability of your CMakeLists.txt files. Using full-line comments or conditional blocks often makes the code clearer than attempting to emulate partial-line comments.
In summary, while CMake does not provide a direct way to comment out a part of a line, you can effectively achieve similar results through conditional statements, variable manipulations, and full-line commenting, which enhances clarity and maintainability in CMake scripts.