A cmake macro for platform dependent setting variable value - cmake

I'm writing a utility macro in cmake for setting a variable dependent on platform. Theoretically it should be simple but I don't know why my variable isn't being set. Here's the macro:
macro(SetCrossPlatform name msvc_val linux_val macos_val)
#macro(SetCrossPlatform VAR name MSVC msvc_val LINUX linux_val MACOS macos_val) # alternative signature that I tried
MESSAGE(STATUS "PLATFORM ${PLATFORM}")
if (PLATFORM STREQUAL "windows-msvc")
set(name ${msvc_val})
elseif (PLATFORM STREQUAL "linux")
set(name ${linux_val})
elseif (PLATFORM STREQUAL "macos")
set(name ${macos_val})
endif ()
endmacro()
which is invoked like:
#SetCrossPlatform(VAR Variable MSVC "microsoft" LINUX "ubuntu" MACOS "apple") # try other signature
SetCrossPlatform(Variable "microsoft" "ubuntu" "apple")
message(STATUS "Variable ${Variable}")
This produces:
-- PLATFORM windows-msvc
-- Variable # <--- Should print out "-- Variable microsoft"
-- Configuring done
-- Generating done
Anybody know what I'm doing wrong?

Inside the macro you need to dereference name for obtain the value of the parameter:
set(${name} ${msvc_val})
By current code
set(name ${msvc_val})
you just define the variable with the name "name".

Related

CMake a few questions about writing my own find_package module

I am a novice in the filed of CMake and I learn how to write my own find_package() module by following the example in the book CMake Cookbook. The following CMakeLists.txt file is provided with the official example.
if(NOT ZeroMQ_ROOT)
set(ZeroMQ_ROOT "$ENV{ZeroMQ_ROOT}")
endif()
if(NOT ZeroMQ_ROOT)
find_path(_ZeroMQ_ROOT NAMES include/zmq.h)
else()
set(_ZeroMQ_ROOT "${ZeroMQ_ROOT}")
endif()
find_path(ZeroMQ_INCLUDE_DIRS NAMES zmq.h HINTS ${_ZeroMQ_ROOT}/include)
if(ZeroMQ_INCLUDE_DIRS)
set(_ZeroMQ_H ${ZeroMQ_INCLUDE_DIRS}/zmq.h)
function(_zmqver_EXTRACT _ZeroMQ_VER_COMPONENT _ZeroMQ_VER_OUTPUT)
set(CMAKE_MATCH_1 "0")
set(_ZeroMQ_expr "^[ \\t]*#define[ \\t]+${_ZeroMQ_VER_COMPONENT}[ \\t]+([0-9]+)$")
file(STRINGS "${_ZeroMQ_H}" _ZeroMQ_ver REGEX "${_ZeroMQ_expr}")
string(REGEX MATCH "${_ZeroMQ_expr}" ZeroMQ_ver "${_ZeroMQ_ver}")
set(${_ZeroMQ_VER_OUTPUT} "${CMAKE_MATCH_1}" PARENT_SCOPE)
endfunction()
_zmqver_EXTRACT("ZMQ_VERSION_MAJOR" ZeroMQ_VERSION_MAJOR)
_zmqver_EXTRACT("ZMQ_VERSION_MINOR" ZeroMQ_VERSION_MINOR)
_zmqver_EXTRACT("ZMQ_VERSION_PATCH" ZeroMQ_VERSION_PATCH)
# We should provide version to find_package_handle_standard_args in the same format as it was requested,
# otherwise it can't check whether version matches exactly.
if(ZeroMQ_FIND_VERSION_COUNT GREATER 2)
set(ZeroMQ_VERSION "${ZeroMQ_VERSION_MAJOR}.${ZeroMQ_VERSION_MINOR}.${ZeroMQ_VERSION_PATCH}")
else()
# User has requested ZeroMQ version without patch part => user is not interested in specific patch =>
# any patch should be an exact match.
set(ZeroMQ_VERSION "${ZeroMQ_VERSION_MAJOR}.${ZeroMQ_VERSION_MINOR}")
endif()
if(NOT ${CMAKE_C_PLATFORM_ID} STREQUAL "Windows")
find_library(ZeroMQ_LIBRARIES
NAMES
zmq
HINTS
${_ZeroMQ_ROOT}/lib
${_ZeroMQ_ROOT}/lib/x86_64-linux-gnu
)
else()
find_library(ZeroMQ_LIBRARIES
NAMES
libzmq
"libzmq-mt-${ZeroMQ_VERSION_MAJOR}_${ZeroMQ_VERSION_MINOR}_${ZeroMQ_VERSION_PATCH}"
"libzmq-${CMAKE_VS_PLATFORM_TOOLSET}-mt-${ZeroMQ_VERSION_MAJOR}_${ZeroMQ_VERSION_MINOR}_${ZeroMQ_VERSION_PATCH}"
libzmq_d
"libzmq-mt-gd-${ZeroMQ_VERSION_MAJOR}_${ZeroMQ_VERSION_MINOR}_${ZeroMQ_VERSION_PATCH}"
"libzmq-${CMAKE_VS_PLATFORM_TOOLSET}-mt-gd-${ZeroMQ_VERSION_MAJOR}_${ZeroMQ_VERSION_MINOR}_${ZeroMQ_VERSION_PATCH}"
HINTS
${_ZeroMQ_ROOT}/lib
)
endif()
endif()
include(FindPackageHandleStandardArgs)
find_package_handle_standard_args(ZeroMQ
FOUND_VAR
ZeroMQ_FOUND
REQUIRED_VARS
ZeroMQ_INCLUDE_DIRS
ZeroMQ_LIBRARIES
VERSION_VAR
ZeroMQ_VERSION
)
I have two questions toward the above example. The first one is that in the function scope _zmqver_EXTRACT we first set the CMAKE_MATCH_1 to 0 and then we do this command set(${_ZeroMQ_VER_OUTPUT} "${CMAKE_MATCH_1}" PARENT_SCOPE). However, it seems that the value of CMAKE_MATCH_1 is always 0. In my opinion, the version information should be stored in the variable ZeroMQ_ver.
What's more, I do not know what the usage of the variable ZeroMQ_FIND_VERSION_COUNT. It seems that this variable is undefined.

CMake: use default value if not provided on second run

When I run for the first run: cmake ..\test2 -DABC=abc
I've got output: ABC=abc
And it is OK, but when I run for the 2nd time: cmake ..\test2 without additional parameter, I still have ABC=abc. I didn't remove any output files.
Is it possible to force cmake to use default value (OFF) of argument if it was provided during next run?
if(ABC)
message(STATUS "abc is set")
else()
message(STATUS "abc is not set")
endif()
doesn't work
CMakeList.txt:
option(ABC "test" )
message(STATUS "ABC=${ABC}")
Is it possible to force CMake to use default value (OFF) of argument?
Yes, just unset the cache variable, which can be done with -U option:
cmake ..\test2 -UABC
So option() finds the variable to be not set and assigns default value to it
In CMake, not using -D means "do not change the variable", not a "do not set the variable at all".

How to specify the variable which must be set and exist in cmake

I have a need to have some variable to be specified and exist in the environment.
In case it does not exist need to stop building.
example
if ( "${VARMUSTEXIST}" STREQUAL "ON" )
message(STATUS is ON)
elif ("${VARMUSTEXIST}" STREQUAL "OFF")
message(STATUS is OFF)
endif()
I don't want to put an if (defined VARMUSTEXIST) everywhere in the script.
In bash there is an option for that "set -u".
Some preliminary points:
if ( "${VARMUSTEXIST}" STREQUAL "ON" ) [...] elif(AGAIN LONG EXPRESSION) [...] endif()normally in cmake is simply: if (VARMUSTEXIST) [...] else() [...] endif()
The command if (DEFINED VARMUSTEXIST) requires DEFINED to be upper case.
You mention bash and environment variables:Environment variables are read using $ENV{VARIABLE_NAME}
For environment variables you will do:
if(NOT DEFINED ENV{VARMUSTEXIST})
message(FATAL_ERROR "You must set VARMUSTEXIST environment variable")
endif()
You say:
I don't want to put an if (defined VARMUSTEXIST) everywhere in the script
This is not clear to me: for each variable you need to check only once, possibly in the main CMakeLists.txt. Of course, you need to add NOT: if (NOT DEFINED VARMUSTEXIST) [stop]
If you can be more precise on your problem, we can design a macro that checks if one or a group of variables are defined or not.
If by environment you mean OS environment variables then the syntax is wrong anyway.
If those are options to be provided by the user, then the literal comparisons with ON and OFF are incorrect, since CMake has more ways to express booleans and they are all in widespread use and became idiomatic. Thus, by expecting either ON or OFF, you're making your build script weird and against everyone's expectations. And you're also making more work for yourself, as you've noticed.
First, you should document the options and give them safe default values using option(). Then it won't ever be that a variable could be undefined.
# early in the top-level CMakeLists.txt
option(VARMUSTEXIST "You can provide it. It exists anyway." NO)
And then you'll check its truth or falsehood rather simply:
# later in top-level file or in subdirectories
if (VARMUSTEXIST)
message("VARMUSTEXIST is true")
else()
message("VARMUSTEXIST is false")
endif()
I think this is the best approach...
CMake Variable:
if(NOT DEFINED VARIABLE)
message(FATAL_ERROR "VARIABLE is not set")
endif(NOT DEFINED VARIABLE)
Environment Variable:
if(NOT DEFINED ENV{VARIABLE})
message(FATAL_ERROR "VARIABLE is not set")
endif(NOT DEFINED ENV{VARIABLE})

cmake invoking dynamic macro name

I have a two macro names, for example:
macro(my_macro1)
# stuff only to use in this macro
endmacro()
macro(my_macro2)
# stuff only to use in this macro
endmacro()
I'd like to dynamic call the macros based a variable name, for example:
if (...)
set (ver 1)
else ()
set (ver 2)
endif ()
my_macro${ver} # this is my idea
Any help?
As #Tsyvarev has commented CMake doesn't support dynamic function names. So here are some alternatives:
Simple Approach
macro(my_macro ver)
if(${ver} EQUAL 1)
my_macro1()
elseif(${ver} EQUAL 2)
my_macro2()
else()
message(FATAL_ERROR "Unsupported macro")
endif()
endmacro()
set(ver 1)
my_macro(ver)
set(ver 2)
my_macro(ver)
A call() Function Implementation
Building on #Fraser work here is a more generic call() function implementation:
function(call _id)
if (NOT COMMAND ${_id})
message(FATAL_ERROR "Unsupported function/macro \"${_id}\"")
else()
set(_helper "${CMAKE_BINARY_DIR}/helpers/macro_helper_${_id}.cmake")
if (NOT EXISTS "${_helper}")
file(WRITE "${_helper}" "${_id}(\$\{ARGN\})\n")
endif()
include("${_helper}")
endif()
endfunction()
set(ver 1)
call(my_macro${ver})
set(ver 2)
call(my_macro${ver})

CMake compare to empty string with STREQUAL failed

I always think that if you want to compare two strings (but not variables) all you need to do is to quote it like that:
if("${A}" STREQUAL "some string")
but now I find out that this code sometimes print oops:
cmake_minimum_required(VERSION 2.8)
if("d" STREQUAL "")
message("oops...")
endif()
May be it's bug (because it prints with Xcode, but not with make)?
Or there is some special variables?
cmake: 2.8.12, 2.8.11.2
xcode: 4.6.2, 5.0.1
Update
There is command string without described problems:
string(COMPARE EQUAL "${A}" "" result)
if(result)
message("...")
endif()
Update 2
The behaviour I've expected implemented since CMake 3.1.0 (see CMP0054).
Output of the 3.0.2 test:
CMake version: 3.0.2
Quoted test
Surprise!
Unquoted test
Surprise!
Output of the 3.1.0 test:
CMake version: 3.1.0
Quoted test
OK
Unquoted test
Surprise!
You ran into a rather annoying "it's not a bug, it's a feature" behavior of CMake. As explained in the documentation of the if command:
The if command was written very early in CMake's history, predating the ${}
variable evaluation syntax, and for convenience evaluates variables named
by its arguments as shown in the above signatures.
Well, the convenience turned out to be an inconvenience. In your example the the string "d" is treated as a variable named d by the if command. If the variable d happens to be defined to the empty string, the message statement will print "oops...", e.g.:
set (d "")
if("d" STREQUAL "")
# this branch will be taken
message("oops...")
else()
message("fine")
endif()
This can give surprising results for statements like
if("${A}" STREQUAL "some string")
because there can be an unintended double expansion of the first argument if the variable A happens to be defined to a string which is also the name of a CMake variable, e.g.:
set (A "d")
set (d "some string")
if("${A}" STREQUAL "some string")
# this branch will be taken
message("oops...")
else()
message("fine")
endif()
Possible work-arounds:
You can add a suffix character to the string after the ${} expansion which prevents the if statement from doing the automatic evaluation:
set (A "d")
set (d "some string")
if("${A} " STREQUAL "some string ")
message("oops...")
else()
# this branch will be taken
message("fine")
endif()
Do not use ${} expansion:
set (A "d")
set (d "some string")
if(A STREQUAL "some string")
message("oops...")
else()
# this branch will be taken
message("fine")
endif()
To prevent unintended evaluation on the right side of STREQUAL use MATCHES with a CMake regular expression instead:
if(A MATCHES "^value$")
...
endif()
Addendum: CMake 3.1 no longer does double expansions for quoted arguments. See the new policy.
As of CMake 3.1, there are new rules variable expansions in if(). They are enabled if you either:
set cmake_minimum_required(3.1) (or higher) at the top of you project file, or
use a lower minimum version number but manually set policy CMP0054 to NEW.
Even in that case, it remains true is that the first argument to if is expanded with the value of a variable matching that name, if it exists:
set (d "")
if(d STREQUAL "")
# this branch will be taken
message("oops...")
else()
message("fine")
endif()
However, this is now disabled if the first argument is quoted:
set (d "")
if("d" STREQUAL "")
message("oops...")
else()
# due to quotes around "d" in if statement,
# this branch will be taken
message("fine")
endif()
If you do want to test a variable's contents against a value, you can either use the classic unquoted syntax, or use the "${d}" syntax you suggested. Thanks to the new rules, this will never suffer the double-expansion problem mentioned in sakra's answer:
set (A "d")
set (d "some string")
if("${A}" STREQUAL "d")
# this branch will be taken
message("fine")
elseif("${A}" STREQUAL "some string")
message("oops...")
else()
message("??")
endif()