I'm using CMake macros to extract the value of certain variables that I want to export as part of my Find-script:
string(REGEX REPLACE "([0-9]+)\\.[0-9]+" "\\1"
MY_PACKAGE_MAJOR_VERSION "${MY_PACKAGE_VERSION}"
How do I cache this variable after determing its value with a macro?
I've tried this:
set(MY_PACKAGE_MAJOR_VERSION ${MY_PACKAGE_MAJOR_VERSION}
CACHE STRING "Major version of my package.")
But without FORCE, it detects that MY_PACKAGE_MAJOR_VERSION is already set, and will thus not set (and thereby cache) the value output from string.
The only workaround I've found is to use an intermediate variable:
string(REGEX REPLACE "([0-9]+)\\.[0-9]+" "\\1"
_MY_PACKAGE_MAJOR_VERSION "${MY_PACKAGE_VERSION}"
set(MY_PACKAGE_MAJOR_VERSION ${_MY_PACKAGE_MAJOR_VERSION}
CACHE STRING "Major version of my package.")
Is there a better way?
Related
Is this the right idiom to discover a variable value and cache it only if it hasn't been cached already? Using the path type is just for example purposes.
IF(NOT $CACHE{PATH_CACHED})
#discover the PATH_CACHED value and store it in PATH_NORMAL
SET(PATH_CACHED ${PATH_NORMAL} CACHE FILEPATH "My path")
ENDIF(NOT $CACHE{PATH_CACHED})
Use if (NOT DEFINED), like so:
if (NOT DEFINED PATH_CACHED)
# do something expensive to compute PATH_CACHED as a normal
# variable
endif ()
set(PATH_CACHED "${PATH_CACHED}"
CACHE FILEPATH "My path")
Two main points here:
Using if (NOT DEFINED X) is a more precise check than if (NOT X) since someone might want to set X to empty.
Unconditionally setting PATH_CACHED to the computed normal variable has more consistent behavior across a range of CMake versions and also preserves the behavior of adjusting a path relative to the process working directory when an untyped cache variable (set on the command line as -DPATH_CACHED=foo) gets a type of PATH or FILEPATH. See the docs here: https://cmake.org/cmake/help/latest/manual/cmake.1.html#cmdoption-cmake-D
Also there hasn't been any need to use all-caps command names or to repeat the condition in endif() for almost twenty years.
I'm currently working on migrating our current build environment from MSBuild to CMake. I have a situation where I need to update the PATH variable in order for the units tests executable to run. This is not a issue for gtest_add_tests, as it uses the source to identify tests. But gtest_discover_tests, which executes the unit tests with the --gtest_list_tests flag, fails to identify any tests because a STATUS_DLL_NOT_FOUND error is encountered during the build.
For example:
add_executable(gTestExe ...)
target_include_directories(gTestExe ...)
target_compile_definitions(gTestExe ...)
target_link_libraries(gTestExe ...)
set (NEWPATH "/path/to/bin;$ENV{PATH}")
STRING(REPLACE ";" "\\;" NEWPATH "${NEWPATH}")
This works:
gtest_add_tests(TARGET gTestExe TEST_LIST allTests)
set_tests_properties(${all_tests} PROPERTIES ENVIRONMENT "PATH=${NEWPATH}")
But this does not:
#set_target_properties(gTestExe PROPERTIES ENVIRONMENT "PATH=${NEWPATH}")
#set_property(DIRECTORY PROPERTY ENVIRONMENT "PATH=${NEWPATH}")
gtest_discover_tests(gTestExe PROPERTIES ENVIRONMENT "PATH=${NEWPATH}")
Edit:
The tests themselves work when added using gtest_add_tests. The issue is the call to discover the tests, during the post build step that gtest_discover_tests registers, fails because the required libraries are not in the PATH.
I came across the same issue this morning and I found a (dirty ?) workaround. The reason why it won't work is a bit complicated, but the workaround is quite simple.
Why it won't work
gtest_discover_tests(gTestExe PROPERTIES ENVIRONMENT "PATH=${NEWPATH}")
Will not work is because the PATH contents are separated by semicolons and therefore are treated by CMake as a list value.
If you look a the GoogleTestAddTests.cmake file (located in C:\Program Files\CMake\share\cmake-3.17\Modules), it treats the PROPERTIES argument with a foreach.
The PROPERTIES value look like this for CMake at this point in the script : ENVIRONMENT;PATH=mypath;mypath2 and will treat mypath2 as a third argument instead of a value for the PATH environment variable.
CMake will then generate the following line :
set_tests_properties( mytest PROPERTIES ENVIRONMENT PATH=mypath mypath2)
Escaping the ; won't work because the list is automatically expended in add_custom_command() in GoogleTest.cmake (l. 420 in cmake 3.17.1) ignoring any form of escaping.
To prevent the cmake foreach to treat each value in the path as a list you can use a bracket argument like :
gtest_discover_tests(gTestExe PROPERTIES ENVIRONMENT "[==[PATH=${NEWPATH}]==]")
The cmake foreach will then treat your argument as one entity. Unfortunately CMake will also put a bracket in the generated code as it contains [ = and maybe spaces :
# This line
if(_arg MATCHES "[^-./:a-zA-Z0-9_]")
set(_args "${_args} [==[${_arg}]==]")
else()
set(_args "${_args} ${_arg}")
endif()
resulting in the following generated script :
set_tests_properties( mytest PROPERTIES ENVIRONMENT [==[ [==[PATH=mypath;mypath2] ]==])
And when executing the test cmake will attempt to read the value only removing the first bracket argument as they don't nest.
Possible workaround
So to do this we need CMake to not use bracket argument on our own bracket argument.
First make a local copy of GoogleTestAddTests.cmake file in your own repository (located in C:\Program Files\CMake\share\cmake-3.17\Modules).
At the beginning of your local copy of GoogleTestAddTests.cmake (l. 12) replace the function add_command by this one :
function(add_command NAME)
set(_args "")
foreach(_arg ${ARGN})
# Patch : allow us to pass a bracket arguments and escape the containing list.
if (_arg MATCHES "^\\[==\\[.*\\]==\\]$")
string(REPLACE ";" "\;" _arg "${_arg}")
set(_args "${_args} ${_arg}")
# end of patch
elseif(_arg MATCHES "[^-./:a-zA-Z0-9_]")
set(_args "${_args} [==[${_arg}]==]")
else()
set(_args "${_args} ${_arg}")
endif()
endforeach()
set(script "${script}${NAME}(${_args})\n" PARENT_SCOPE)
endfunction()
This will make cmake don't use bracket list on our bracket list and automatically escape the ; as set_tests_properties also treat the ; as a list.
Finally we need CMake to use our custom GoogleTestAddTests.cmake instead of the one in CMake.
After your call to include(GoogleTest) set the variable _GOOGLETEST_DISCOVER_TESTS_SCRIPT to the path to your local GoogleTestAddTests.cmake :
# Need google test
include(GoogleTest)
# Use our own version of GoogleTestAddTests.cmake
set(_GOOGLETEST_DISCOVER_TESTS_SCRIPT
${CMAKE_CURRENT_LIST_DIR}/GoogleTestAddTests.cmake
)
Note : In my example the GoogleTestAddTests.cmake is right next to the processing cmake file.
Then a simple call to
gtest_discover_tests(my_target
PROPERTIES ENVIRONMENT "[==[PATH=${my_path};$ENV{PATH}]==]"
)
should work.
I have a file version.txt
VERSION_MAJOR 1
VERSION_MINOR 1
VERSION_PATCH 3
I want to use cmake to add a definition for major, minor and patch.
I've tries using
file(STRING "version.txt" myvar)
but this just puts the whole file in myvar.
How do I get the numbers?
Your use of file is incorrect, you want to use READ in order to read the contents of the file into a variable.
file(READ "version.txt" ver)
Once you have the file's contents into a variable, you can then use REGEX MATCH with a capture group, and access the capture group using CMAKE_MATCH_N
REGEX MATCH:
Create a regular expression with a capture group which will capture the numbers following "VERSION_MAJOR":
string(REGEX MATCH "VERSION_MAJOR ([0-9]*)" _ ${ver})
Note that if the regex matches the input variable, the entire match will be stored in the output variable. However, we don't want the entire match (as that includes the string "VERSION_MAJOR"), so I've just used a variable name _ as the output variable, which, by convention, tells the user I am not interested in this variable
CMAKE_MATCH_N:
If the match is successful, then the capture groups are available in CMAKE_MATCH_N. In this instance there is only one capture group, so we want to use CMAKE_MATCH_1
set(ver_major ${CMAKE_MATCH_1})
At this point ver_major contains just the major version no.
You can then repeat this for the other version components.
Full example below:
cmake_minimum_required(VERSION 3.5)
file(READ "version.txt" ver)
string(REGEX MATCH "VERSION_MAJOR ([0-9]*)" _ ${ver})
set(ver_major ${CMAKE_MATCH_1})
string(REGEX MATCH "VERSION_MINOR ([0-9]*)" _ ${ver})
set(ver_minor ${CMAKE_MATCH_1})
string(REGEX MATCH "VERSION_PATCH ([0-9]*)" _ ${ver})
set(ver_patch ${CMAKE_MATCH_1})
message("version: ${ver_major}.${ver_minor}.${ver_patch}")
Output:
$ cmake .
version: 1.1.3
-- Configuring done
-- Generating done
-- Build files have been written to: /tmp
For production code you would obviously want to make the cmake script more robust by checking whether the match was successful, and emitting an error if not.
I'm asking this as a reminder to myself the next time I use CMake. It never sticks, and Google results aren't great.
What's the syntax to set and use variables in CMake?
When writing CMake scripts there is a lot you need to know about the syntax and how to use variables in CMake.
The Syntax
Strings using set():
set(MyString "Some Text")
set(MyStringWithVar "Some other Text: ${MyString}")
set(MyStringWithQuot "Some quote: \"${MyStringWithVar}\"")
Or with string():
string(APPEND MyStringWithContent " ${MyString}")
Lists using set():
set(MyList "a" "b" "c")
set(MyList ${MyList} "d")
Or better with list():
list(APPEND MyList "a" "b" "c")
list(APPEND MyList "d")
Lists of File Names:
set(MySourcesList "File.name" "File with Space.name")
list(APPEND MySourcesList "File.name" "File with Space.name")
add_excutable(MyExeTarget ${MySourcesList})
The Documentation
CMake/Language Syntax
CMake: Variables Lists Strings
CMake: Useful Variables
CMake set() Command
CMake string()Command
CMake list() Command
Cmake: Generator Expressions
The Scope or "What value does my variable have?"
First there are the "Normal Variables" and things you need to know about their scope:
Normal variables are visible to the CMakeLists.txt they are set in and everything called from there (add_subdirectory(), include(), macro() and function()).
The add_subdirectory() and function() commands are special, because they open-up their own scope.
Meaning variables set(...) there are only visible there and they make a copy of all normal variables of the scope level they are called from (called parent scope).
So if you are in a sub-directory or a function you can modify an already existing variable in the parent scope with set(... PARENT_SCOPE)
You can make use of this e.g. in functions by passing the variable name as a function parameter. An example would be function(xyz _resultVar) is setting set(${_resultVar} 1 PARENT_SCOPE)
On the other hand everything you set in include() or macro() scripts will modify variables directly in the scope of where they are called from.
Second there is the "Global Variables Cache". Things you need to know about the Cache:
If no normal variable with the given name is defined in the current scope, CMake will look for a matching Cache entry.
Cache values are stored in the CMakeCache.txt file in your binary output directory.
The values in the Cache can be modified in CMake's GUI application before they are generated. Therefore they - in comparison to normal variables - have a type and a docstring. I normally don't use the GUI so I use set(... CACHE INTERNAL "") to set my global and persistant values.
Please note that the INTERNAL cache variable type does imply FORCE
In a CMake script you can only change existing Cache entries if you use the set(... CACHE ... FORCE) syntax. This behavior is made use of e.g. by CMake itself, because it normally does not force Cache entries itself and therefore you can pre-define it with another value.
You can use the command line to set entries in the Cache with the syntax cmake -D var:type=value, just cmake -D var=value or with cmake -C CMakeInitialCache.cmake.
You can unset entries in the Cache with unset(... CACHE).
The Cache is global and you can set them virtually anywhere in your CMake scripts. But I would recommend you think twice about where to use Cache variables (they are global and they are persistant). I normally prefer the set_property(GLOBAL PROPERTY ...) and set_property(GLOBAL APPEND PROPERTY ...) syntax to define my own non-persistant global variables.
Variable Pitfalls and "How to debug variable changes?"
To avoid pitfalls you should know the following about variables:
Local variables do hide cached variables if both have the same name
The find_... commands - if successful - do write their results as cached variables "so that no call will search again"
Lists in CMake are just strings with semicolons delimiters and therefore the quotation-marks are important
set(MyVar a b c) is "a;b;c" and set(MyVar "a b c") is "a b c"
The recommendation is that you always use quotation marks with the one exception when you want to give a list as list
Generally prefer the list() command for handling lists
The whole scope issue described above. Especially it's recommended to use functions() instead of macros() because you don't want your local variables to show up in the parent scope.
A lot of variables used by CMake are set with the project() and enable_language() calls. So it could get important to set some variables before those commands are used.
Environment variables may differ from where CMake generated the make environment and when the the make files are put to use.
A change in an environment variable does not re-trigger the generation process.
Especially a generated IDE environment may differ from your command line, so it's recommended to transfer your environment variables into something that is cached.
Sometimes only debugging variables helps. The following may help you:
Simply use old printf debugging style by using the message() command. There also some ready to use modules shipped with CMake itself: CMakePrintHelpers.cmake, CMakePrintSystemInformation.cmake
Look into CMakeCache.txt file in your binary output directory. This file is even generated if the actual generation of your make environment fails.
Use variable_watch() to see where your variables are read/written/removed.
Look into the directory properties CACHE_VARIABLES and VARIABLES
Call cmake --trace ... to see the CMake's complete parsing process. That's sort of the last reserve, because it generates a lot of output.
Special Syntax
Environment Variables
You can can read $ENV{...} and write set(ENV{...} ...) environment variables
Generator Expressions
Generator expressions $<...> are only evaluated when CMake's generator writes the make environment (it comparison to normal variables that are replaced "in-place" by the parser)
Very handy e.g. in compiler/linker command lines and in multi-configuration environments
References
With ${${...}} you can give variable names in a variable and reference its content.
Often used when giving a variable name as function/macro parameter.
Constant Values (see if() command)
With if(MyVariable) you can directly check a variable for true/false (no need here for the enclosing ${...})
True if the constant is 1, ON, YES, TRUE, Y, or a non-zero number.
False if the constant is 0, OFF, NO, FALSE, N, IGNORE, NOTFOUND, the empty string, or ends in the suffix -NOTFOUND.
This syntax is often use for something like if(MSVC), but it can be confusing for someone who does not know this syntax shortcut.
Recursive substitutions
You can construct variable names using variables. After CMake has substituted the variables, it will check again if the result is a variable itself. This is very powerful feature used in CMake itself e.g. as sort of a template set(CMAKE_${lang}_COMPILER ...)
But be aware this can give you a headache in if() commands. Here is an example where CMAKE_CXX_COMPILER_ID is "MSVC" and MSVC is "1":
if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "MSVC") is true, because it evaluates to if("1" STREQUAL "1")
if(CMAKE_CXX_COMPILER_ID STREQUAL "MSVC") is false, because it evaluates to if("MSVC" STREQUAL "1")
So the best solution here would be - see above - to directly check for if(MSVC)
The good news is that this was fixed in CMake 3.1 with the introduction of policy CMP0054. I would recommend to always set cmake_policy(SET CMP0054 NEW) to "only interpret if() arguments as variables or keywords when unquoted."
The option() command
Mainly just cached strings that only can be ON or OFF and they allow some special handling like e.g. dependencies
But be aware, don't mistake the option with the set command. The value given to option is really only the "initial value" (transferred once to the cache during the first configuration step) and is afterwards meant to be changed by the user through CMake's GUI.
References
How is CMake used?
cmake, lost in the concept of global variables (and PARENT_SCOPE or add_subdirectory alternatives)
Looping over a string list
How to store CMake build settings
CMake compare to empty string with STREQUAL failed
When should I quote CMake variables?
Here are a couple basic examples to get started quick and dirty.
One item variable
Set variable:
SET(INSTALL_ETC_DIR "etc")
Use variable:
SET(INSTALL_ETC_CROND_DIR "${INSTALL_ETC_DIR}/cron.d")
Multi-item variable (ie. list)
Set variable:
SET(PROGRAM_SRCS
program.c
program_utils.c
a_lib.c
b_lib.c
config.c
)
Use variable:
add_executable(program "${PROGRAM_SRCS}")
CMake docs on variables
$ENV{FOO} for usage, where FOO is being picked up from the environment variable. otherwise use as ${FOO}, where FOO is some other variable. For setting, SET(FOO "foo") would be used in CMake.
I have added a subdirectory in CMake by using add_subdirectory. How can I access a variable from the scope of that subdirectory without explicitly setting the variable by using set in combination with PARENT_SCOPE ?
set(BOX2D_BUILD_STATIC 1)
set(BOX2D_BUILD_EXAMPLES 0)
set(BOX2D_INSTALL_BY_DEFAULT 0)
add_subdirectory(Box2D_v2.2.1)
message(STATUS "Using Box2D version ${BOX2D_VERSION}")
# how to get ${BOX2D_VERSION} variable without modifying CMakeLists.txt in Box2D_v2.2.1?
Is this possible?
If the variable is a plain variable (as opposed to a cache variable), there is no way to access it from the parent scope.
Cache variables (those set with set(... CACHE ...)) can be accessed regardless of scope, as can global properties (set_property(GLOBAL ...)).
While #Angew's answer is correct, there aren't many things that are really impossible with CMake :-)
If you have a line like
set(BOX2D_VERSION 2.2.1)
in Box2D_v2.2.1/CMakeLists.txt, then you can retrieve the version in the parent scope by doing something like:
file(STRINGS Box2D_v2.2.1/CMakeLists.txt VersionSetter
REGEX "^[ ]*set\\(BOX2D_VERSION")
string(REGEX REPLACE "(^[ ]*set\\(BOX2D_VERSION[ ]*)([^\\)]*)\\)" "\\2"
BOX2D_VERSION ${VersionSetter})
This is a bit fragile; it doesn't accommodate for extra spaces in the set command for example, or cater for the value being set twice. You could cater for these possibilities too, but if you know the format of the set command and it's unlikely to change, then this is a reasonable workaround.