macro

Start recording a macro for later invocation as a command

macro(<name> [<arg1> ...])
  <commands>
endmacro()

Defines a macro named <name> that takes arguments named <arg1>, … Commands listed after macro, but before the matching endmacro(), are not executed until the macro is invoked.

Per legacy, the endmacro() command admits an optional <name> argument. If used, it must be a verbatim repeat of the argument of the opening macro command.

See the cmake_policy() command documentation for the behavior of policies inside macros.

See the Macro vs Function section below for differences between CMake macros and functions.

Invocation

The macro invocation is case-insensitive. A macro defined as

macro(foo)
  <commands>
endmacro()

can be invoked through any of

foo()
Foo()
FOO()
cmake_language(CALL foo)

and so on. However, it is strongly recommended to stay with the case chosen in the macro definition. Typically macros use all-lowercase names.

The cmake_language(CALL ...) command can also be used to invoke the macro.

Arguments

When a macro is invoked, the commands recorded in the macro are first modified by replacing formal parameters (${arg1}, …) with the arguments passed, and then invoked as normal commands.

In addition to referencing the formal parameters you can reference the values ${ARGC} which will be set to the number of arguments passed into the function as well as ${ARGV0}, ${ARGV1}, ${ARGV2}, … which will have the actual values of the arguments passed in. This facilitates creating macros with optional arguments.

Furthermore, ${ARGV} holds the list of all arguments given to the macro and ${ARGN} holds the list of arguments past the last expected argument. Referencing to ${ARGV#} arguments beyond ${ARGC} have undefined behavior. Checking that ${ARGC} is greater than # is the only way to ensure that ${ARGV#} was passed to the function as an extra argument.

Macro vs Function

The macro command is very similar to the function() command. Nonetheless, there are a few important differences.

In a function, ARGN, ARGC, ARGV and ARGV0, ARGV1, … are true variables in the usual CMake sense. In a macro, they are not, they are string replacements much like the C preprocessor would do with a macro. This has a number of consequences, as explained in the Argument Caveats section below.

Another difference between macros and functions is the control flow. A function is executed by transferring control from the calling statement to the function body. A macro is executed as if the macro body were pasted in place of the calling statement. This has the consequence that a return() in a macro body does not just terminate execution of the macro; rather, control is returned from the scope of the macro call. To avoid confusion, it is recommended to avoid return() in macros altogether.

Unlike a function, the CMAKE_CURRENT_FUNCTION, CMAKE_CURRENT_FUNCTION_LIST_DIR, CMAKE_CURRENT_FUNCTION_LIST_FILE, CMAKE_CURRENT_FUNCTION_LIST_LINE variables are not set for a macro.

Argument Caveats

Since ARGN, ARGC, ARGV, ARGV0 etc. are not variables, you will NOT be able to use commands like

if(ARGV1) # ARGV1 is not a variable
if(DEFINED ARGV2) # ARGV2 is not a variable
if(ARGC GREATER 2) # ARGC is not a variable
foreach(loop_var IN LISTS ARGN) # ARGN is not a variable

In the first case, you can use if(${ARGV1}). In the second and third case, the proper way to check if an optional variable was passed to the macro is to use if(${ARGC} GREATER 2). In the last case, you can use foreach(loop_var ${ARGN}) but this will skip empty arguments. If you need to include them, you can use

set(list_var "${ARGN}")
foreach(loop_var IN LISTS list_var)

Note that if you have a variable with the same name in the scope from which the macro is called, using unreferenced names will use the existing variable instead of the arguments. For example:

macro(bar)
  foreach(arg IN LISTS ARGN)
    <commands>
  endforeach()
endmacro()

function(foo)
  bar(x y z)
endfunction()

foo(a b c)

Will loop over a;b;c and not over x;y;z as one might have expected. If you want true CMake variables and/or better CMake scope control you should look at the function command.