Help: Clarify that ARGV# beyond ARGC will have an undefined behavior (#15380)

parent e3363bfb
......@@ -24,6 +24,10 @@ This facilitates creating functions with optional arguments.
Additionally ``ARGV`` holds the list of all arguments given to the
function 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.
A function opens a new scope: see :command:`set(var PARENT_SCOPE)` for
details.
......
......@@ -24,6 +24,10 @@ This facilitates creating macros with optional arguments.
Additionally ``${ARGV}`` holds the list of all arguments given to the
macro and ``${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.
See the :command:`cmake_policy()` command documentation for the behavior
of policies inside macros.
......@@ -37,10 +41,15 @@ replacements much like the C preprocessor would do with a macro.
Therefore 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 case, you can
use ``foreach(loop_var ${ARGN})`` but this will skip empty arguments.
In the first case, you can use ``if(${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}")
......
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