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How to Define Function Inside Macro In Cmake?

5 minutes read

To define a function inside a macro in CMake, you can use the function() command to create a new CMake function and then call that function from within your macro. By defining a function within a macro, you can encapsulate a set of commands and reuse them in multiple places within your CMake scripts.


Here's an example of how you can define a function inside a macro in CMake:

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macro(my_macro)
    function(my_function)
        message("Inside my_function")
    endfunction()

    my_function()
endmacro()

my_macro()


In this example, the my_macro macro defines a new function called my_function using the function() command. The my_function function simply outputs a message using the message() command. The my_macro macro then calls the my_function function.


What is a function in CMake?

In CMake, a function is a reusable piece of code that can be called multiple times with different arguments. Functions in CMake are defined using the function() command and can take parameters that are specified when the function is called. Functions can be used to encapsulate and modularize code, making it easier to manage and reuse code across a CMake project.


What is the syntax for defining a function in CMake?

The syntax for defining a function in CMake is as follows:

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function(function_name ARG1 ARG2)
    # function body
endfunction()


  • "function_name" is the name of the function being defined.
  • "ARG1", "ARG2", etc. are the arguments that the function can accept.
  • The function body consists of CMake commands that will be executed when the function is called.


Here is an example of defining and using a function in CMake:

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function(print_message MESSAGE)
    message("Message: ${MESSAGE}")
endfunction()

print_message("Hello, World!")


When executing this CMake script, the function print_message will be called with the argument "Hello, World!", and it will output "Message: Hello, World!" to the console.


How to define a function that modifies global variables in CMake?

To define a function in CMake that modifies global variables, you can use the set() command to set the global variables inside the function. Here is an example of how you can define a function that modifies global variables in CMake:

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# Define a function that modifies global variables
function(modify_global_variables)
    set(GLOBAL_VAR1 "value1" PARENT_SCOPE)
    set(GLOBAL_VAR2 "value2" PARENT_SCOPE)
endfunction()

# Call the function to modify global variables
modify_global_variables()

# Print the modified global variables
message("GLOBAL_VAR1 = ${GLOBAL_VAR1}")
message("GLOBAL_VAR2 = ${GLOBAL_VAR2}")


In this example, the modify_global_variables function sets the values of GLOBAL_VAR1 and GLOBAL_VAR2 global variables using the set() command with the PARENT_SCOPE option. The PARENT_SCOPE option allows the variables to be modified in the parent scope, making them global variables.


You can then call the modify_global_variables function to modify the global variables and print their values using the message() command.


What is the difference between a macro and a function in CMake?

In CMake, a macro and a function are both used to define reusable blocks of code, but they have some key differences:

  1. Parameters: A function in CMake can have named parameters that are passed into the function and accessed using those names inside the function. A macro, on the other hand, uses a special variable called ARGN to access all provided arguments without named parameters.
  2. Scope: Functions in CMake have their own scope, meaning that any variables declared inside a function are local to that function and not visible outside of it. Macros, on the other hand, do not introduce a new scope and any variables declared inside a macro are visible in the calling scope.
  3. Argument parsing: Functions in CMake have stricter argument parsing rules, meaning that you must provide the correct number of arguments and types when calling a function. Macros, on the other hand, are more flexible in their argument parsing and can handle a varying number of arguments.
  4. Expansion: Functions in CMake are expanded at the point where they are called, which can be useful for scoping purposes. Macros, on the other hand, are expanded in-place wherever they are defined.


In general, functions are more robust and provide better scoping and argument handling, while macros are more flexible and can be used in a wider variety of situations.


What is the role of functions in the CMake scripting language?

Functions in CMake are used to encapsulate a set of commands and logic to perform a specific operation or task. They help in organizing and modularizing CMake scripts, making them more readable, maintainable, and reusable.


Functions can be defined using the function() command and called using the call() command. They can take arguments, have local variables, and return values.


Some common use cases of functions in CMake scripting are:

  1. Creating reusable logic for configuring and building targets.
  2. Abstracting complex configuration tasks (e.g., setting compiler flags, including headers and libraries).
  3. Implementing conditional logic based on input parameters.
  4. Streamlining repetitive tasks across multiple CMake scripts.


Overall, functions play a crucial role in simplifying the scripting process and improving the structure and organization of CMake projects.


How to define a function that is compatible with older versions of CMake?

To define a function that is compatible with older versions of CMake, you can use the macro() command instead of function(). Macros are similar to functions but have different scoping rules that may be more suitable for compatibility with older versions of CMake. Here is an example definition of a function using the macro() command:

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macro(my_function arg1 arg2)
  message("Argument 1: ${arg1}")
  message("Argument 2: ${arg2}")
endmacro()

# Call the macro
my_function("Hello" "World")


By using the macro() command instead of function(), you can ensure compatibility with older versions of CMake that may not support all features of the function() command. Remember that macros have different scoping rules compared to functions, so make sure to adjust your code accordingly.

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