Let's say I have some protobuf related cmake code as a library that resides inside CMakeLists.pro file and I need to include this library as a external file configuration. How to do that ?
I think this question is asking how to make cmake modules. IE you have helper code and would like to make it easily available.
A normal top level project has a top level cmake folder. Here is an example of what that would look like.
cmake
tests
src
.gitignore
CMakeLists.txt
README.md
Inside the cmake folder say you have a cmake module called foo.cmake
(It's important to make the file end with .cmake file extension)
Anyway this is what your foo.cmake may look like
# Include guards need at least cmake 3.10
include_guard() # Good practice to use an include_guard()
function(bar)
...
endfunction()
Now in your main cmakelists how do you call this function? Simple.
cmake_minimum_required(VERSION 3.18)
# Add the cmake folder to the cmake module path, this makes it easier to include files
list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake/")
# Include foo.cmake
include(foo)
# Call the bar function you defined in foo.cmake
bar()
And that's how you can refer to external cmake file from the main CMakeLists.txt
Related
I have a submodule with a CMakeLists.txt, which I would like to "amend" in a way to make it work for my specific purpose (I need to add compiler flags and a different output directory) The output is a static library. My current approach is as follows:
I have a CMakeLists.txt in the root directory, which adds the submodule CMakeLists.txt via add_subdirectory() like so:
set(CMAKE_CXX_FLAGS "-my_needed_flags "
add_subdirectory(SubmoduleLibrary)
set_target_properties(SubmoduleLibrary PROPERTIES ARCHIVE_OUTPUT_DIRECTORY output_folder)
add_custom_target(BuildLib)
add_dependencies(BuildLib SubmoduleLibrary)
Now this seems to work in some ways (the output directory is correctly chosen). But I get linker errors which I don't get when I compile the library adding the flags etc to the original CMakeLists.txt.
What is the correct way to build a library from an existing CMakeLists.txt with added parameters?
I've recently began experimenting with CMake, and have written a simple Hello, World program in C++.
Here is my directory structure:
CMakeLists.txt
src/
CMakeLists.txt
main.cpp
build/
The top-level CMakeLists.txt reads as follows:
#Require at least CMake version 2.8
cmake_minimum_required(VERSION 2.8 FATAL_ERROR)
#set up the project name, version and language to compile in
project(HelloWorld)
#tell CMake that we have some source files located in the src directory
add_subdirectory(src)
And the CMakeLists.txt in /src reads:
add_executable(helloworld
main.cpp)
install(TARGETS helloworld
RUNTIME DESTINATION ../build)
Now, I would expect that these two scripts would cause the makefile to create the helloworld binary in the /build directory, but after running make, it creates the helloworld binary in /build/src.
If I move the add_executable and install function calls into the top-level CMakeLists.txt, then the helloworld binary is placed in /build, not /build/src.
So, as I understand, it places the build in the folder relative to where CMake was invoked. Why does it appear as though install is doing nothing, then?
Additionally, what if I have multiple complex subdirectories?
How should I write out my CMakeLists.txt while avoiding file(GLOB ...)?
For example;
CMakeLists.txt
/build
/src
/class_A
a.hpp
a.cpp
/class_B
b.hpp
b.cpp
/class_CB
cb.hpp
cb.cpp
/class_D
d.hpp
d.cpp
Would I just have a giant list of .cpp files, all with relative paths to each cpp file, and pass that list into the add_executable(executable ${SOURCE_FILES})? Or is there an easier way with using multiple CMakeLists.txt?
You misinterpret the install command. It is used to install your files, for example with make install.
When you configure your project, CMake will mimic the structure of your project. This means all folders are created in the same structure and the binaries appear in the according build directories.
Either place your targets in the main directory, which I would consider bad stile. Better live with build/src or give it a more meaningful name.
I have the following directory structure and library dependencies:
./lib-a
./lib-b (depending on lib-a)
Each directory contains a CMakeLists.txt file for generating its own library.
I am using an out-of-source building policy.
In order to say that lib-b depends on lib-a, I have put the command add_subdirectory(../lib-a lib-a) in ./lib-b/CMakeLists.txt, according to what is taught by the official CMake tutorial. This way I obtain that a subdirectory lib-a is created in ./lib-b/build dir.
This is not the behaviour I desire. What I would like to obtain is CMake making reference to lib-a in generating lib-b and, if lib-a has not been already generated, CMake should generate it inside ./lib-a/build by using the CMakeLists.txt of lib-a (in a behaviour similar to the one of the make tool when dealing with dependencies).
I would also like to add that I am not using a root CMakeLists.txt in my example, but what I would like to have is the lib-b/CMakeLists.txt declaring the dependency on lib-a, thus making lib-a to be compiled, if not already, by using its own lib-a/CMakeLists.txt.
Here is the dirs structure and their contents:
lib-a/
CMakeLists.txt (for compiling lib-a)
src/
test.cpp
include/
test.hpp
lib-b/
main.cpp
CMakeLists.txt (for compiling lib-b; here is the point where I would like to make reference to lib-a, that I need for the generation of lib-b)
lib-b/main.cpp contains also an include of test.hpp of lib-a, because it is using a function of lib-a. This should be taken into consideration in the specification of lib-b/CMakeLists.txt.
What should the content of the two lib-a/CMakeLists.txt and lib-b/CMakeLists.txt files be?
I think you misunderstand the tutorial. The thing that links the libraries together is target_link_library(lib_b lib_a). If the name of the dependency is a library that is part of the build, CMake will magically make the dependencies work. It has nothing to do with subdirectories. In fact, if I have the following directory structure:
./
./a.hpp
./a.cpp
./b.hpp
./b.cpp
./CMakeLists.txt
The following will set the dependencies just fine:
PROJECT(lib_a)
ADD_LIBRARY(lib_a a.hpp a.cpp)
PROJECT(lib_b)
ADD_LIBRARY(lib_b b.hpp b.cpp)
TARGET_LINK_LIBRARIES(lib_b lib_a)
This will work across subdirectory projects as well:
./
./CMakeLists.txt
./lib_a/CMakeLists.txt
./lib_a/a.hpp
./lib_a/a.cpp
./lib_b/CMakeLists.txt
./lib_b/b.hpp
./lib_b/b.cpp
And the list files:
# ./CMakeLists.txt
CMAKE_MINIMUM_REQUIRED(VERSION 2.8)
ADD_SUBDIRECTORY(lib_a)
ADD_SUBDIRECTORY(lib_b)
# ./lib_a/CMakeLists.txt
CMAKE_MINIMUM_REQUIRED(VERSION 2.8)
PROJECT(lib_a)
ADD_LIBRARY(lib_a a.hpp a.cpp)
# ./lib_b/CMakeLists.txt
CMAKE_MINIMUM_REQUIRED(VERSION 2.8)
PROJECT(lib_b)
INCLUDE_DIRECTORIES(${lib_a_SOURCE_DIR})
ADD_LIBRARY(lib_b b.hpp b.cpp)
TARGET_LINK_LIBRARIES(lib_b lib_a)
I'm using the FindProtobuf module in a project where the protocol buffer files are in a sub-directory. I want the CMakeLists.txt file in that sub-directory to invoke protoc to generate the CPP Files. My project folder structure is like this:
cammy/CMakeLists.txt # Root CMakeLists.txt
cammy/protofiles/test.proto # protofile
cammy/protofiles/CMakeLists.txt
I have the include(FindProtobuf), the find_package invocation and the call to PROTOBUF_GENERATE_CPP in the CMakeLists.txt file in protobuf folder.
The executable build step is in the Root CMakeLists.txt file and I add the generated files
to the target executable in this file
ie.
add_executable( ${EXEC} ${SRCS} ${PROTO_SRC} ${PROTO_HEADER} )
target_link_libraries( ${EXEC} ${PROTOBUF_LIBRARIES} )
are both defined in the root CMakeLists.txt
When I run cmake, it does not run protoc to generate the Source files even though I expilicitly tie generated sources to the executable thereby creating a dependency.
When I move all the contents of CMakeLists.txt in the protofiles folder into the root CMakeLists.txt, the proto files are compiled.
Can anyone help me with this? I want all the protocol buffer building stuff to go in the CMakeLists.txt file created in the protofiles folder.
I also noticed that variables generated in the inner CMakeLists.txt ( like PROTO_SRC ) are defined in the inner file when printed ( ie I get the correct generated CPP filename ) but when I print the same variable in the root file.. it is empty. Its almost as though I need to "export" (if there were a way in cmake ) the variables out to the root folder.
Any help would be much appreciated.
Thanks
Kartik
I think [FindProtobuf][0] isn't really meant to be used this way. From its docs:
NOTE: The PROTOBUF_GENERATE_CPP macro & add_executable() or add_library()
calls only work properly within the same directory.
You're trying to use the PROTOBUF_GENERATE_CPP macro in a subdirectory, and although the CMake docs don't really make it clear, a subdirectory introduces a new scope for variables. This means that any variables set or modified in the subdir scope don't affect similarly-named variables in the parent scope. Hence the reason for PROTO_SRC being available in your protofiles dir, but not in the parent.
The way to pass variables up a scope is to use [set(... PARENT_SCOPE)][1], so in protofiles/CMakeLists.txt you could do:
PROTOBUF_GENERATE_CPP(PROTO_SRC PROTO_HEADER test.proto)
set(PROTOBUF_INCLUDE_DIRS ${PROTOBUF_INCLUDE_DIRS} PARENT_SCOPE)
set(PROTOBUF_LIBRARIES ${PROTOBUF_LIBRARIES} PARENT_SCOPE)
set(PROTO_SRC ${PROTO_SRC} PARENT_SCOPE)
set(PROTO_HEADER ${PROTO_HEADER} PARENT_SCOPE)
However, this still doesn't get us all the way!
CMake doesn't actually invoke the protoc compiler to generate the .pb.h and .pb.cc files - it uses [add_custom_command][2] to do this. The custom command specifies the .pb.h and .pb.cc files as outputs, and the custom command is only invoked (i.e. protoc executed) if a subsequent target which depends on these files is built.
So, at configure time (when CMake executes) these files don't exist. This is a problem if you try to add them as sources to an add_library or add_executable command - CMake needs to be told that these files don't exist when it runs, but that they will exist at build time.
The way to do that is to set the [GENERATED][3] property to TRUE for these files. The PROTOBUF_GENERATE_CPP macro does that automatically, but as with the variables, the property isn't populated up into the parent scope. So in your top-level CMakeLists.txt, you also need to add:
set_source_files_properties(${PROTO_SRC} ${PROTO_HEADER} PROPERTIES
GENERATED TRUE)
As you can see, using PROTOBUF_GENERATE_CPP in a different dir to the corresponding add_library/add_executable commands is a bit fragile. If you can avoid doing it, you probably should.
[0]: https://cmake.org/cmake/help/latest/module/FindProtobuf.html "CMake latest documentation for "FindProtobuf" module"
[1]: https://cmake.org/cmake/help/latest/command/set.html "CMake latest documentation for "set" command"
[2]: https://cmake.org/cmake/help/latest/command/add_custom_command.html "CMake latest documentation for "add_custom_command""
[3]: https://cmake.org/cmake/help/latest/prop_sf/GENERATED.html "CMake latest documentation for "GENERATED" source file property"
I'm writing a cmake file for a project which has the following structure
project/ (root)
libraries/ (contains (precompiled) libraries
src/
code/ (contains a set of fortran files)
My CMakeLists.txt file is currently in project/ and effectively is just
cmake_minimum_required(VERSION 2.6)
enable_language(Fortran)
project(project1)
set(projsrc src/code)
set(libdir lib/)
find_library(PROJ_LIBRARY pr10 PATHS ${libdir})
add_executable (sc1 sc1.f90)
target_link_libraries(sc1 ${PROJ_LIBRARY})
This creates my binary in the same folder as the source code, when I actually want it in the level above (i.e. in the src folder - this structure will be changed so we have a bin folder eventually), but haven't worked out how to do it.
Some answers on SO say you have to have a CMakeLists.txt file in every folder - is this correct? Is it possible to set an environment variable or use a CMake variable (e.g. http://cmake.org/cmake/help/v2.8.8/cmake.html#command:set). It's also not very clear from some answers whether the solutions they have posted are C++ specific (as that is what language CMake most often seems to be used for).
Edit
I found out that I can change it to the behaviour I want by modifying it slightly:
cmake_minimum_required(VERSION 2.6)
enable_language(Fortran)
project(project1)
set(projsrc src/code)
set(libdir lib/)
find_library(PROJ_LIBRARY pr10 PATHS ${libdir})
add_executable (src/sc1 ${projsrc}/sc1.f90)
target_link_libraries(src/sc1 ${PROJ_LIBRARY})
However, this doesn't explain why my behaviour is different to how it should be, according to arrowdodger below. I'm also still trying to work out how to display the values of environment variables; I've tried the following with no luck:
message(${RUNTIME_OUTPUT_DIRECTORY})
message($ENV{RUNTIME_OUTPUT_DIRECTORY})
message(${CMAKE_RUNTIME_OUTPUT_DIRECTORY})
message($ENV{CMAKE_RUNTIME_OUTPUT_DIRECTORY})
By default, binaries will appear in respective subdirectory of your build dir. By respective i mean the directory that contains CMakeLists.txt with add_executable() call.
For example, if you have following CMakeLists.txt
add_executable(tgt1 src1.f90)
add_executable(tgt2 subdir/src2.f90)
in the root folder, you will get both binaries in ${CMAKE_BINARY_DIR}. So if you wish tgt2 to be in ${CMAKE_BINARY_DIR}/subdir, you need to add CMakeLists.txt there and call add_executable(tgt2 src2.f90) from there.
You can change this behavior:
CMAKE_LIBRARY_OUTPUT_DIRECTORY, CMAKE_RUNTIME_OUTPUT_DIRECTORY and others.
You can also set respective target properties.