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Currently I have a directory structure that looks like the following
.
├── CMakeLists.txt
├── Base
│ ├── CMakeLists.txt
│ ├── include
│ │ └── base.h
│ └── src
│ └── base.cpp
├── Derived
│ ├── CMakeLists.txt
│ ├── include
│ │ └── derived.h
│ └── src
│ └── derived.cpp
└── src
└── main.cpp
and the CMakeLists.txt files looking like
./CMakeLists.txt
cmake_minimum_required(VERSION 3.1)
set(CMAKE_CXX_STANDARD 11)
project(MyProj)
add_subdirectory(Base)
add_subdirectory(Derived)
add_executable(main src/main.cpp)
target_link_libraries(main Base)
target_link_libraries(main Derived)
./Base/CMakeLists.txt
add_library(Base STATIC src/base.cpp)
target_include_directories(Base PUBLIC include)
./Derived/CMakeLists.txt
add_library(Derived STATIC src/derived.cpp)
target_include_directories(Derived PUBLIC include)
target_link_libraries(Derived Base)
I want to know if this is an appropriate way to structure a CMake project when using inheritance in C++. If there is a more idiomatic way to structure this, I am open to suggestions.
If your intention is to build two libraries, and an executable, then that is what your structure achieves. I would however recommend thinking why you are doing that, and perhaps consider whether it would be simpler to instead have both classes in a single library.
If I keep extending this, say make another class that inherits from Derived, then I have to make a new CMakeLists.txt file then link and include against these files. I don't have a problem doing this, but it does not seem very maintainable for larger projects
No, you don't have to make a new CMakeLists.txt unless you add a new target. You don't necessarily need more than a single target for a project.
A target (be it executable or a library) is not limited to having only one translation unit.
My personal preference for small project is three (or two) targets: A library containing all functionality, a main executable with int main() that does nothing except invoke the library (if the project is an executable rather than just the library), and a test executable with int main() from a test framework. The library can optionally be split to smaller pieces if it has parts that are reusable in other projects.
set(CMAKE_CXX_STANDARD 11)
prefer target specific properties instead:
set_target_properties(
Base PROPERTIES
CXX_STANDARD 11
# use unless you also support older standards
CXX_STANDARD_REQUIRED ON
)
The dependees will inherit the property, but you can set it explicitly in each for potentially lesser chance of breakage in case you later decide to not use the base library.
Creating a library for each class is overkill and might slow down compilation on some build systems.
On some of my projects, I have over 300 types, not counting templates and lambdas. I cannot imagine creating a library for each classes.
I want to know if this is an appropriate way to structure a CMake project when using inheritance in C++
The features you are using should not change how the code is organised physically. Instead, base your file layout in logical self contained part of your code with clear dependencies between each parts.
The only nitpick: Use this form to link libraries together:
target_link_libraries(main PUBLIC Base) # or private
The rest of your CMake make good use of the target based API. The only thing I would change would be to be less fine grained in term of what constitute a library.
I am trying to create a reasonable library structure and CMake file which would allow other CMake projects to easily include this library. I've found a lot of similar questions, however, none of them seems to address my exact problem.
My current structure is the following:
/*MyLibrary/
├── CMakeLists.txt (including lib subdirectories)
├── external/
│ └── googletest/
├── lib/
│ ├── common/
│ │ ├── CMakeList.txt (creates static lib common)
│ │ ├── include/common/*.h
│ │ └── src/*.cpp
│ ├── cipher/
│ │ ├── CMakeList.txt (creates static lib cipher)
│ │ ├── include/cipher/*.h
│ │ └── src/*.cpp
└── test/
├── main.cpp (code for executing google test)
├── CMakeLists.txt (creates unittest executable)
├── common/*Test.cpp
└── cipher/*Test.cpp
*/
Now I want to create a project with a similar directory structure but the problem occurs when I want to create a static library in that project with the same name as one of the static libraries in MyLibrary (common for example).
I was thinking of including the library into the project using add_subdirectory(external/MyLibrary) in the projects CMakeLists, but that fails because the names of the static libraries collide.
Even when I solve this issue by renaming the library (which I don't in fact believe is an elegant solution), I end up with googletest conflicts because both, the library and my project, are dependent on googletest.
Is there any way to solve this easily? I was thinking of 2 possibilities:
In the MyLibrary I would create one static library from all the sub-libraries called libMyLibrary.aand include only that library (preferred option, but I don't have a clue how to achieve it in CMake)
Forcing the users of the library to install it and don't include the library as a project submodule (last option I would go for)
Is there some other reasonable way to solve it which would make my library compatible with most CMake projects? If not, how can I achieve at least one of the mentioned options?
In short: how can I create a CMake file for a library so the library is easy to include in other CMake projects?
How can I deal with redundant dependencies such as googletest?
How can I create a CMake file for a library so the library is easy to include in other CMake projects?
There is no universal approach for that purpose.
By including your project into another one with add_subdirectory(), you "open" internals of your project to other one. Aside of advantage in having the library's target ready for linking, this approach has disadvantages too. Target's collisions, cached variables collisions will be your headache, among with some other problems.
If you want your project to be included into other with add_subdirectory, avoid using "generic" names for your targets. E.g., use <my_project_name>_common instead of common.
Some targets you cannot rename (like gtest). If those targets aren't really required for your project to work, create an option for disable them:
option(<my_project_name>_TESTING "Enable testing" ON)
if(<my_project_name>_TESTING)
add_subdirectory(external/googletest)
endif()
See also my answer to the similar question about targets' names collision.
I am currently working on a C++ project using CMake as its build system.
The projects consists of several output executables, each having relatively little custom code, but leveraging a few common libraries:
programX
|
├── CMakeLists.txt (this contains the main executable targets)
|
├── Engine
│ ├── ...
│ ├── CMakeLists.txt
|
├── Utils
│ ├── third_party (this is what I added)
│ │ └── backward-cpp
│ | └ CMakeLists.txt
│ ├── ...
│ └── CMakeLists.txt
|
└── etc.
The main functionality of the project is contained inside an Engine library which is statically linked to the main executables using something like target_link_libraries(programX Engine). Many utilities are also contained in a separate Utils library.
I have added a CMake dependency to one of these project libraries (it's the backward-cpp stacktrace prettifier). That project is also built using CMake.
In the interest of modularity, I have added the backward-cpp project as a dependency to the only project library which actually uses it, Utils. I did this in order not to "pollute" the main CMakeLists.txt file with directives only pertaining to a small part of the project.
My Utils/CMakeLists.txt therefore looks like this:
SET(UTILS_HEADERS ...)
set(UTILS_OBJECTS Dummy.cpp ${UTILS_HEADERS})
# This is the new dependency!
add_subdirectory(third_party/backward-cpp)
SOURCE_GROUP("" FILES ${UTILS_HEADERS})
# 'BACKWARD_ENABLE' and 'add_backward' are needed for linking.
add_library(Utils ${UTILS_OBJECTS} ${BACKWARD_ENABLE})
add_backward(Utils)
Doing this, however, does not work, and the project ends up not linking (the symbols from the backward-cpp library are not found), unless I link the output executables to the third party library directly, in the root CMakeLists.txt file (add_backward(MainExecutableA-Z)).
I am aware that one cannot link static libraries to other static libraries, but I would be interested in knowing if there is a nice way to achieve this modularization of static libraries and their dependencies using CMake.
(Alternatively, I could always just link everything directly to the main targets, since that always works.)
Update (May 22nd 2017)
I've managed to get everything working now, with backwards-cpp being controlled 100% from the "narrowest" CMakeLists.txt file, thanks to the helpful answers I got. Here's the Utils/CMakeLists.txt file I ended up with (non-relevant parts removed):
SET(UTILS_HEADERS ...)
SET(UTILS_SOURCES ...)
# If enabled, enables sensible stack traces on Linux, complete with corresponding source
# code, where available. CUDA errors also produce complete stack traces when this is on.
# If disabled, the error messages degrade gracefully to file/line information.
OPTION(WITH_BACKWARDS_CPP "Build with backwards-cpp stack trace dumping library? (Linux-only)" TRUE)
message(STATUS "backwards-cpp-enhanced stack traces? " ${WITH_BACKWARDS_CPP})
if(WITH_BACKWARDS_CPP)
# Support 'backward-cpp,' a lean stacktrace printing library for Linux.
add_definitions(-DWITH_BACKWARDS_CPP)
add_subdirectory(third_party/backward-cpp)
endif()
SOURCE_GROUP("" FILES ${UTILS_HEADERS} ${UTILS_SOURCES})
add_library(Utils ${UTILS_HEADERS} ${UTILS_SOURCES})
# ...unrelated CUDA stuff...
if(WITH_BACKWARDS_CPP)
# Link agains libbfd to ensure backward-cpp can extract additional information from the binary,
# such as source code mappings. The '-lbfd' dependency is optional, and if it is disabled, the
# stack traces will still work, but won't show unmangled symbol names or source code snippets.
# You may need to set BACKWARD_USE_BFD to 0 in its `hpp` and `cpp` files to avoid linker errors.
target_link_libraries(Utils PUBLIC -lbfd)
target_link_libraries(Utils PUBLIC backward)
endif()
After looking inside the BackwardConfig.cmake and reading the project's README I came to the conclusion that the most easy way to link your executable with the Backward-cpp is using the add_backward(target) macro as you mentioned in your question.
The other option described under Modifying CMAKE_MODULE_PATH subtitle in the README shuld work as well but I not tested. The find_package in Config mode will search for file called <name>Config.cmake which is BackwardConfig.cmake in this case, so you don't have to write any extra CMake modules like FindBackward.cmake. As a try I would do the following:
set(UTILS_HEADERS ...)
set(UTILS_OBJECTS Dummy.cpp ${UTILS_HEADERS})
source_group("" FILES ${UTILS_HEADERS})
add_library(Utils ${UTILS_OBJECTS})
list(APPEND CMAKE_MODULE_PATH /path/to/backward-cpp)
find_package(Backward)
target_link_libraries(Utils PUBLIC Backward::Backward)
After reading the README of backward-cpp, I would try the following (only the last two lines change):
SET(UTILS_HEADERS ...)
set(UTILS_OBJECTS Dummy.cpp ${UTILS_HEADERS})
# This is the new dependency!
add_subdirectory(third_party/backward-cpp)
SOURCE_GROUP("" FILES ${UTILS_HEADERS})
add_library(Utils ${UTILS_OBJECTS})
target_link_libraries(Utils PUBLIC backward)
Note that PUBLIC in the last statement takes care of setting the include directories and link libraries when you link other targets against Utils.
I'm using gnu make, and gcc for compiling. I'm on linux (Ubuntu)
Here is a diagram for the game black jack where the nodes represent eventual object files.
I have organized the code where each class is in it's own folder.
tree -d
.
└── classes
├── dealer
│ └── hand
├── deck
│ └── card
│ ├── card_color
│ ├── card_suit
│ ├── card_value
│ └── colorizer
├── discard_pile
│ └── card
├── user
│ └── hand
│ └── card
└── user_choice
In order to make the file-system behave like a graph, some directories are symbolic links.
There is no repeated code.
For example, if the actual card code is in the directory deck, then the hand and discard_pile folders have a symbolic link to that directory in them.
I have run into multiple definition errors, because my program links against all the sub directory object files.
It will follow symbolic links and end up gathering some object files more than once.
I can't tell it to ignore symbolically linked folders, because sometimes they need to be followed.
For example: if I were to make a driver program in the dealer folder, it would need to gather the hand,card,card_color,card_suit,card_value,colorizer objects (even though the hand folder is a symbolic link).
Is there a way to continue gathering duplicate object files, but to tell gcc or make to ignore the duplicates before linking?
Because they are symbolic links, the path names are different.
Also, there may be instances where objects are named the same, but are different implementations.
I'm not sure how to identify that duplicate object files are indeed the same file and should not be linked more than once.
I don't want to make this question too general by asking for advice on how to manage big and expanding projects (where entity relationships are complicated), but if you think my structure is nonsensical or problematic, please point out the problems and other ways you would go about it. I was trying to avoid having all my source files in one directory, because without class diagrams, the relationships would be difficult to derive.
Just becuse you USE the same function multiple times in different contexts doesn't mean you need to link it more than once.
Your card.cpp needs to go into a common location that can be used by all your different components.
Typically, a project will have a set of header files, and a set of source files (.cpp or .c for example). When I work on small projects - less than about a dozen source files, I just keep all the files in one directory. But there's nothing wrong with keeping it a bit more split up. However, a file should only be in one place in the directory structure [!!NO LINKS!!].
Header files are either with their respective source files, or in a separate "include" directory.
Typically, source files don't "care" where the header files are, they are just "somewhere". Instead you tell the compiler to look for headers in "../some-component" with -I ../some-component.
And each source file is only compiled and linked once, to form the final binary.
I am new to programming in general so I decided that I would start by making a simple vector class in C++. However I would like to get in to good habits from the start rather than trying to modify my workflow later on.
I currently have only two files vector3.hpp and vector3.cpp. This project will slowly start to grow (making it much more of a general linear algebra library) as I become more familiar with everything, so I would like to adopt a "standard" project layout to make life easier later on. So after looking around I have found two ways to go about organizing hpp and cpp files, the first being:
project
└── src
├── vector3.hpp
└── vector3.cpp
and the second being:
project
├── inc
│ └── project
│ └── vector3.hpp
└── src
└── vector3.cpp
Which would you recommend and why?
Secondly I would like to use the Google C++ Testing Framework for unit testing my code as it seems fairly easy to use. Do you suggest bundling this with my code, for example in a inc/gtest or contrib/gtest folder? If bundled, do you suggest using the fuse_gtest_files.py script to reduce the number or files, or leaving it as is? If not bundled how is this dependency handled?
When it comes to writing tests, how are these generally organized? I was thinking to have one cpp file for each class (test_vector3.cpp for example) but all compiled in to one binary so that they can all be run together easily?
Since the gtest library is generally build using cmake and make, I was thinking that it would make sense for my project to also be built like this? If I decided to use the following project layout:
├── CMakeLists.txt
├── contrib
│ └── gtest
│ ├── gtest-all.cc
│ └── gtest.h
├── docs
│ └── Doxyfile
├── inc
│ └── project
│ └── vector3.cpp
├── src
│ └── vector3.cpp
└── test
└── test_vector3.cpp
How would the CMakeLists.txt have to look so that it can either build just the library or the library and the tests? Also I have seen quite a few projects that have a build and a bin directory. Does the build happen in the build directory and then the binaries moved out in to the bin directory? Would the binaries for the tests and the library live in the same place? Or would it make more sense to structure it as follows:
test
├── bin
├── build
└── src
└── test_vector3.cpp
I would also like to use doxygen to document my code. Is it possible to get this to automatically run with cmake and make?
Sorry for so many questions, but I have not found a book on C++ that satisfactorily answers these type of questions.
C++ build systems are a bit of a black art and the older the project
the more weird stuff you can find so it is not surprising that a lot
of questions come up. I'll try to walk through the questions one by one and mention some general things regarding building C++ libraries.
Separating headers and cpp files in directories. This is only
essential if you are building a component that is supposed to be used
as a library as opposed to an actual application. Your headers are the
basis for users to interact with what you offer and must be
installed. This means they have to be in a subdirectory (no-one wants
lots of headers ending up in top-level /usr/include/) and your
headers must be able to include themselves with such a setup.
└── prj
├── include
│ └── prj
│ ├── header2.h
│ └── header.h
└── src
└── x.cpp
works well, because include paths work out and you can use easy
globbing for install targets.
Bundling dependencies: I think this largely depends on the ability of
the build system to locate and configure dependencies and how
dependent your code on a single version is. It also depends on how
able your users are and how easy is the dependency to install on their
platform. CMake comes with a find_package script for Google
Test. This makes things a lot easier. I would go with bundling only
when necessary and avoid it otherwise.
How to build: Avoid in-source builds. CMake makes out of source-builds
easy and it makes life a lot easier.
I suppose you also want to use CTest to run tests for your system (it
also comes with build-in support for GTest). An important decision for
directory layout and test organization will be: Do you end up with
subprojects? If so, you need some more work when setting up CMakeLists
and should split your subprojects into subdirectories, each with its
own include and src files. Maybe even their own doxygen runs and
outputs (combining multiple doxygen projects is possible, but not easy
or pretty).
You will end up with something like this:
└── prj
├── CMakeLists.txt <-- (1)
├── include
│ └── prj
│ ├── header2.hpp
│ └── header.hpp
├── src
│ ├── CMakeLists.txt <-- (2)
│ └── x.cpp
└── test
├── CMakeLists.txt <-- (3)
├── data
│ └── testdata.yyy
└── testcase.cpp
where
(1) configures dependencies, platform specifics and output paths
(2) configures the library you are going to build
(3) configures the test executables and test-cases
In case you have sub-components I would suggest adding another hierarchy and use the tree above for each sub-project. Then things get tricky, because you need to decide if sub-components search and configure their dependencies or if you do that in the top-level. This should be decided on a case-by-case basis.
Doxygen: After you managed to go through the configuration dance of
doxygen, it is trivial to use CMake add_custom_command to add a
doc target.
This is how my projects end up and I have seen some very similar projects, but of course this is no cure all.
Addendum At some point you will want to generate a config.hpp
file that contains a version define and maybe a define to some version
control identifier (a Git hash or SVN revision number). CMake has
modules to automate finding that information and to generate
files. You can use CMake's configure_file to replace variables in a
template file with variables defined inside the CMakeLists.txt.
If you are building libraries you will also need an export define to
get the difference between compilers right, e.g. __declspec on MSVC
and visibility attributes on GCC/clang.
As a starter, there are some conventional names for directories that you cannot ignore, these are based on the long tradition with the Unix file system. These are:
trunk
├── bin : for all executables (applications)
├── lib : for all other binaries (static and shared libraries (.so or .dll))
├── include : for all header files
├── src : for source files
└── doc : for documentation
It is probably a good idea to stick to this basic layout, at least at the top-level.
About splitting the header files and source files (cpp), both schemes are fairly common. However, I tend to prefer keeping them together, it is just more practical on day-to-day tasks to have the files together. Also, when all the code is under one top-level folder, i.e., the trunk/src/ folder, you can notice that all the other folders (bin, lib, include, doc, and maybe some test folder) at the top level, in addition to the "build" directory for an out-of-source build, are all folders that contain nothing more than files that are generated in the build process. And thus, only the src folder needs to be backed up, or much better, kept under a version control system / server (like Git or SVN).
And when it comes to installing your header files on the destination system (if you want to eventually distribute your library), well, CMake has a command for installing files (implicitly creates a "install" target, to do "make install") which you can use to put all the headers into the /usr/include/ directory. I just use the following cmake macro for this purpose:
# custom macro to register some headers as target for installation:
# setup_headers("/path/to/header/something.h" "/relative/install/path")
macro(setup_headers HEADER_FILES HEADER_PATH)
foreach(CURRENT_HEADER_FILE ${HEADER_FILES})
install(FILES "${SRCROOT}${CURRENT_HEADER_FILE}" DESTINATION "${INCLUDEROOT}${HEADER_PATH}")
endforeach(CURRENT_HEADER_FILE)
endmacro(setup_headers)
Where SRCROOT is a cmake variable that I set to the src folder, and INCLUDEROOT is cmake variable that I configure to wherever to headers need to go. Of course, there are many other ways to do this, and I'm sure my way is not the best. The point is, there is no reason to split the headers and sources just because only the headers need to be installed on the target system, because it is very easy, especially with CMake (or CPack), to pick out and configure the headers to be installed without having to have them in a separate directory. And this is what I have seen in most libraries.
Quote: Secondly I would like to use the Google C++ Testing Framework for unit testing my code as it seems fairly easy to use. Do you suggest bundling this with my code, for example in a "inc/gtest" or "contrib/gtest" folder? If bundled, do you suggest using the fuse_gtest_files.py script to reduce the number or files, or leaving it as is? If not bundled how is this dependency handled?
Don't bundle dependencies with your library. This is generally a pretty horrible idea, and I always hate it when I'm stuck trying to build a library that did that. It should be your last resort, and beware of the pitfalls. Often, people bundle dependencies with their library either because they target a terrible development environment (e.g., Windows), or because they only support an old (deprecated) version of the library (dependency) in question. The main pitfall is that your bundled dependency might clash with already installed versions of the same library / application (e.g., you bundled gtest, but the person trying to build your library already has a newer (or older) version of gtest already installed, then the two might clash and give that person a very nasty headache). So, as I said, do it at your own risk, and I would say only as a last resort. Asking the people to install a few dependencies before being able to compile your library is a much lesser evil than trying to resolve clashes between your bundled dependencies and existing installations.
Quote: When it comes to writing tests, how are these generally organised? I was thinking to have one cpp file for each class (test_vector3.cpp for example) but all compiled in to one binary so that they can all be run together easily?
One cpp file per class (or small cohesive group of classes and functions) is more usual and practical in my opinion. However, definitely, don't compile them all into one binary just so that "they can all be run together". That's a really bad idea. Generally, when it comes to coding, you want to split things up as much as it is reasonable to do so. In the case of unit-tests, you don't want one binary to run all the tests, because that means that any little change that you make to anything in your library is likely to cause a near total recompilation of that unit-test program, and that's just minutes / hours lost waiting for recompilation. Just stick to a simple scheme: 1 unit = 1 unit-test program. Then, use either a script or a unit-test framework (such as gtest and/or CTest) to run all the test programs and report to failure/success rates.
Quote: Since the gtest library is generally build using cmake and make, I was thinking that it would make sense for my project to also be built like this? If I decided to use the following project layout:
I would rather suggest this layout:
trunk
├── bin
├── lib
│ └── project
│ └── libvector3.so
│ └── libvector3.a products of installation / building
├── docs
│ └── Doxyfile
├── include
│ └── project
│ └── vector3.hpp
│_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
│
├── src
│ └── CMakeLists.txt
│ └── Doxyfile.in
│ └── project part of version-control / source-distribution
│ └── CMakeLists.txt
│ └── vector3.hpp
│ └── vector3.cpp
│ └── test
│ └── test_vector3.cpp
│_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
│
├── build
└── test working directories for building / testing
└── test_vector3
A few things to notice here. First, the sub-directories of your src directory should mirror the sub-directories of your include directory, this is just to keep things intuitive (also, try to keep your sub-directory structure reasonably flat (shallow), because deep nesting of folders is often more of a hassle than anything else). Second, the "include" directory is just an installation directory, its contents are just whatever headers are picked out of the src directory.
Third, the CMake system is intended to be distributed over the source sub-directories, not as one CMakeLists.txt file at the top-level. This keeps things local, and that's good (in the spirit of splitting things up into independent pieces). If you add a new source, a new header, or a new test program, all you need is to edit one small and simple CMakeLists.txt file in the sub-directory in question, without affecting anything else. This also allows you to restructure the directories with ease (CMakeLists are local and contained in the sub-directories being moved). The top-level CMakeLists should contain most of the top-level configurations, such as setting up destination directories, custom commands (or macros), and finding packages installed on the system. The lower-level CMakeLists should contain only simple lists of headers, sources, and unit-test sources, and the cmake commands that register them to compilation targets.
Quote: How would the CMakeLists.txt have to look so that it can either build just the library or the library and the tests?
Basic answer is that CMake allows you to specifically exclude certain targets from "all" (which is what is built when you type "make"), and you can also create specific bundles of targets. I can't do a CMake tutorial here, but it is fairly straight forward to find out by yourself. In this specific case, however, the recommended solution is, of course, to use CTest, which is just an additional set of commands that you can use in the CMakeLists files to register a number of targets (programs) that are marked as unit-tests. So, CMake will put all the tests in a special category of builds, and that is exactly what you asked for, so, problem solved.
Quote: Also I have seen quite a few projects that have a build ad a bin directory. Does the build happen in the build directory and then the binaries moved out in to the bin directory? Would the binaries for the tests and the library live in the same place? Or would it make more sense to structure it as follows:
Having a build directory outside the source ("out-of-source" build) is really the only sane thing to do, it is the de facto standard these days. So, definitely, have a separate "build" directory, outside the source directory, just as the CMake people recommend, and as every programmer I have ever met does. As for the bin directory, well, that is a convention, and it is probably a good idea to stick to it, as I said in the beginning of this post.
Quote: I would also like to use doxygen to document my code. Is it possible to get this to automatically run with cmake and make?
Yes. It is more than possible, it is awesome. Depending on how fancy you want to get, there are several possibilities. CMake does have a module for Doxygen (i.e., find_package(Doxygen)) which allows you to register targets that will run Doxygen on some files. If you want to do more fancy things, like updating the version number in the Doxyfile, or automatically entering a date / author stamps for source files and so on, it is all possible with a bit of CMake kung-fu. Generally, doing this will involve that you keep a source Doxyfile (e.g., the "Doxyfile.in" that I put in the folder layout above) which has tokens to be found and replaced by CMake's parsing commands. In my top-level CMakeLists file, you will find one such piece of CMake kung-fu that does a few fancy things with cmake-doxygen together.
Structuring the project
I would generally favour the following:
├── CMakeLists.txt
|
├── docs/
│ └── Doxyfile
|
├── include/
│ └── project/
│ └── vector3.hpp
|
├── src/
└── project/
└── vector3.cpp
└── test/
└── test_vector3.cpp
This means that you have a very clearly defined set of API files for your library, and the structure means that clients of your library would do
#include "project/vector3.hpp"
rather than the less explicit
#include "vector3.hpp"
I like the structure of the /src tree to match that of the /include tree, but that's personal preference really. However, if your project expands to contain subdirectories within /include/project, it would generally help to match those inside the /src tree.
For the tests, I favour keeping them "close" to the files they test, and if you do end up with subdirectories within /src, it's a pretty easy paradigm for others to follow if they want to find a given file's test code.
Testing
Secondly I would like to use the Google C++ Testing Framework for unit testing my code as it seems fairly easy to use.
Gtest is indeed simple to use and is fairly comprehensive in terms of its capabilities. It can be used alongside gmock very easily to extend its capabilities, but my own experiences with gmock have been less favourable. I'm quite prepared to accept that this may well be down to my own shortcomings, but gmock tests tends to be more difficult to create, and much more fragile / difficult to maintain. A big nail in the gmock coffin is that it really doesn't play nice with smart pointers.
This is a very trivial and subjective answer to a huge question (which probably doesn't really belong on S.O.)
Do you suggest bundling this with my code, for example in a "inc/gtest" or "contrib/gtest" folder? If bundled, do you suggest using the fuse_gtest_files.py script to reduce the number or files, or leaving it as is? If not bundled how is this dependency handled?
I prefer using CMake's ExternalProject_Add module. This avoids you having to keep gtest source code in your repository, or installing it anywhere. It is downloaded and built in your build tree automatically.
See my answer dealing with the specifics here.
When it comes to writing tests, how are these generally organised? I was thinking to have one cpp file for each class (test_vector3.cpp for example) but all compiled in to one binary so that they can all be run together easily?
Good plan.
Building
I'm a fan of CMake, but as with your test-related questions, S.O. is probably not the best place to ask for opinions on such a subjective issue.
How would the CMakeLists.txt have to look so that it can either build just the library or the library and the tests?
add_library(ProjectLibrary <All library sources and headers>)
add_executable(ProjectTest <All test files>)
target_link_libraries(ProjectTest ProjectLibrary)
The library will appear as a target "ProjectLibrary", and the test suite as a target "ProjectTest". By specifying the library as a dependency of the test exe, building the test exe will automatically cause the library to be rebuilt if it is out of date.
Also I have seen quite a few projects that have a build ad a bin directory. Does the build happen in the build directory and then the binaries moved out in to the bin directory? Would the binaries for the tests and the library live in the same place?
CMake recommends "out-of-source" builds, i.e. you create your own build directory outside the project and run CMake from there. This avoids "polluting" your source tree with build files, and is highly desirable if you're using a vcs.
You can specify that the binaries are moved or copied to a different directory once built, or that they are created by default in another directory, but there's generally no need. CMake provides comprehensive ways to install your project if desired, or make it easy for other CMake projects to "find" the relevant files of your project.
With regards to CMake's own support for finding and executing gtest tests, this would largely be inappropriate if you build gtest as part of your project. The FindGtest module is really designed to be used in the case where gtest has been built separately outside of your project.
CMake provides its own test framework (CTest), and ideally, every gtest case would be added as a CTest case.
However, the GTEST_ADD_TESTS macro provided by FindGtest to allow easy addition of gtest cases as individual ctest cases is somewhat lacking in that it doesn't work for gtest's macros other than TEST and TEST_F. Value- or Type-parameterised tests using TEST_P, TYPED_TEST_P, etc. aren't handled at all.
The problem doesn't have an easy solution that I know of. The most robust way to get a list of gtest cases is to execute the test exe with the flag --gtest_list_tests. However, this can only be done once the exe is built, so CMake can't make use of this. Which leaves you with two choices; CMake must try to parse C++ code to deduce the names of the tests (non-trivial in the extreme if you want to take into account all gtest macros, commented-out tests, disabled tests), or test cases are added by hand to the CMakeLists.txt file.
I would also like to use doxygen to document my code. Is it possible to get this to automatically run with cmake and make?
Yes - although I have no experience on this front. CMake provides FindDoxygen for this purpose.
In addition to the other (excellent) answers, I am going to describe a structure I've been using for relatively large-scale projects.
I am not going to address the subquestion about Doxygen, since I would just repeat what is said in the other answers.
Rationale
For modularity and maintainability, the project is organized as a set of small units.
For clarity, let's name them UnitX, with X = A, B, C, ... (but they can have any general name).
The directory structure is then organized to reflect this choice, with the possibility to group units if necessary.
Solution
The basic directory layout is the following (content of units is detailed later on):
project
├── CMakeLists.txt
├── UnitA
├── UnitB
├── GroupA
│ └── CMakeLists.txt
│ └── GroupB
│ └── CMakeLists.txt
│ └── UnitC
│ └── UnitD
│ └── UnitE
project/CMakeLists.txt could contain the following:
cmake_minimum_required(VERSION 3.0.2)
project(project)
enable_testing() # This will be necessary for testing (details below)
add_subdirectory(UnitA)
add_subdirectory(UnitB)
add_subdirectory(GroupA)
and project/GroupA/CMakeLists.txt:
add_subdirectory(GroupB)
add_subdirectory(UnitE)
and project/GroupB/CMakeLists.txt:
add_subdirectory(UnitC)
add_subdirectory(UnitD)
Now to the structure of the different units (let's take, as an example, UnitD)
project/GroupA/GroupB/UnitD
├── README.md
├── CMakeLists.txt
├── lib
│ └── CMakeLists.txt
│ └── UnitD
│ └── ClassA.h
│ └── ClassA.cpp
│ └── ClassB.h
│ └── ClassB.cpp
├── test
│ └── CMakeLists.txt
│ └── ClassATest.cpp
│ └── ClassBTest.cpp
│ └── [main.cpp]
To the different components:
I like having source (.cpp) and headers (.h) in the same folder. This avoids a duplicate directory hierarchy, makes maintenance easier. For installation, it is no problem (especially with CMake) to just filter the header files.
The role of the directory UnitD is to later on allow including files with #include <UnitD/ClassA.h>. Also, when installing this unit, you can just copy the directory structure as is. Note that you can also organize your source files in subdirectories.
I like a README file to summarize what the unit is about and specify useful information about it.
CMakeLists.txt could simply contain:
add_subdirectory(lib)
add_subdirectory(test)
lib/CMakeLists.txt:
project(UnitD)
set(headers
UnitD/ClassA.h
UnitD/ClassB.h
)
set(sources
UnitD/ClassA.cpp
UnitD/ClassB.cpp
)
add_library(${TARGET_NAME} STATIC ${headers} ${sources})
# INSTALL_INTERFACE: folder to which you will install a directory UnitD containing the headers
target_include_directories(UnitD
PUBLIC $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>
PUBLIC $<INSTALL_INTERFACE:include/SomeDir>
)
target_link_libraries(UnitD
PUBLIC UnitA
PRIVATE UnitC
)
Here, note that it is not necessary to tell CMake that we want the include directories for UnitA and UnitC, as this was already specified when configuring those units. Also, PUBLIC will tell all targets that depend on UnitD that they should automatically include the UnitA dependency, while UnitC won't be required then (PRIVATE).
test/CMakeLists.txt (see further below if you want to use GTest for it):
project(UnitDTests)
add_executable(UnitDTests
ClassATest.cpp
ClassBTest.cpp
[main.cpp]
)
target_link_libraries(UnitDTests
PUBLIC UnitD
)
add_test(
NAME UnitDTests
COMMAND UnitDTests
)
Using GoogleTest
For Google Test, the easiest is if its source is present in somewhere your source directory, but you don't have to actually add it there yourself.
I've been using this project to download it automatically, and I wrap its usage in a function to make sure that it is downloaded only once, even though we have several test targets.
This CMake function is the following:
function(import_gtest)
include (DownloadProject)
if (NOT TARGET gmock_main)
include(DownloadProject)
download_project(PROJ googletest
GIT_REPOSITORY https://github.com/google/googletest.git
GIT_TAG release-1.8.0
UPDATE_DISCONNECTED 1
)
set(gtest_force_shared_crt ON CACHE BOOL "" FORCE) # Prevent GoogleTest from overriding our compiler/linker options when building with Visual Studio
add_subdirectory(${googletest_SOURCE_DIR} ${googletest_BINARY_DIR} EXCLUDE_FROM_ALL)
endif()
endfunction()
and then, when I want to use it inside one of my test targets, I will add the following lines to the CMakeLists.txt (this is for the example above, test/CMakeLists.txt):
import_gtest()
target_link_libraries(UnitDTests gtest_main gmock_main)