clang-uml - C++ UML diagram generator based on Clang and PlantUML

clang-uml is an automatic C++ to PlantUML class, sequence and package diagram generator, driven by YAML configuration files. The main idea behind the project is to easily maintain up-to-date diagrams within a code-base or document legacy code. The configuration file or files for clang-uml define the type and contents of each generated diagram.

clang-uml currently supports C++ up to version 17.

Current master version (and any release since 0.2.0) has been refactored to use Clang LibTooling instead of libclang. Previous version is available in branch 0.1.x, however it is not maintained.

Features

Main features supported so far include:

• Class diagram generation
  • Basic class properties and methods including visibility
  • Class relationships including associations, aggregations, dependencies and friendship
  • Template instantiation relationships
  • Relationship inference from C++ containers and smart pointers
  • Diagram content filtering based on namespaces, elements and relationships
  • Optional package generation from namespaces
  • Interactive links to online code to classes, methods and class fields in SVG diagrams
• Sequence diagram generation
  • Generation of sequence diagram from one code location to another (currently only for non-template code)
• Package diagram generation
  • Generation of package diagram based on C++ namespaces
  • Interactive links to online code to packages
• Include graph diagram generation
  • Show include graph for selected files

To see what clang-uml can do so far, checkout the diagrams generated for unit test cases here and examples in clang-uml-examples repository.

Installation

Distribution packages

Ubuntu

sudo add-apt-repository ppa:bkryza/clang-uml
sudo apt update
sudo apt install clang-uml

Conda

conda config --add channels conda-forge
conda config --set channel_priority strict
conda install -c bkryza/label/clang-uml clang-uml

Building from source

First make sure that you have the following dependencies installed:

# Ubuntu (clang version will vary depending on Ubuntu version)
apt install ccache cmake libyaml-cpp-dev clang-12 libclang-12-dev libclang-cpp12-dev

# macos
brew install ccache cmake llvm yaml-cpp

Then proceed with building the sources:

git clone https://github.com/bkryza/clang-uml
cd clang-uml
# Please note that top level Makefile is just a convenience wrapper for CMake
make release
release/clang-uml --help

# To build using a specific installed version of LLVM use:
LLVM_VERSION=14 make release

# Optionally
make install
# or
export PATH=$PATH:$PWD/release

# On macos, it is necessary to build clang-uml using the same llvm against which it is linked, e.g.
export CC=/usr/local/opt/llvm/bin/clang
export CCX=/usr/local/opt/llvm/bin/clang++
LLVM_VERSION=14 make release

Usage

Generating compile commands database

clang-uml requires an up-to-date compile_commands.json file, containing the list of commands used for compiling the source code. Nowadays, this file can be generated rather easily using multiple methods:

• For CMake projects, simply invoke the cmake command as cmake -DCMAKE_EXPORT_COMPILE_COMMANDS=ON ...
• For Make projects checkout compiledb or Bear
• For Boost-based projects try commands_to_compilation_database
• For SCons, invoke compilation_db tool (requires SCons > 4.0.0)

Invocation

By default, config-uml will assume that the configuration file .clang-uml and compilation database compile_commands.json files are in the current directory, so if they are in the top level directory of a project, simply run:

clang-uml

The output path for diagrams, as well as alternative location of compilation database can be specified in .clang-uml configuration file.

For other options checkout help:

clang-uml --help

Configuration file format and examples

Configuration files are written in YAML, and provide a list of diagrams which should be generated by clang-uml. Basic example is as follows:

compilation_database_dir: .
output_directory: puml
diagrams:
  myproject_class:
    type: class
    glob:
      - src/*.cc
    using_namespace:
      - myproject
    include:
      namespaces:
        - myproject
    exclude:
      namespaces:
        - myproject::detail
    plantuml:
      after:
        - 'note left of {{ alias("MyProjectMain") }}: Main class of myproject library.'

See here for detailed configuration file reference guide.

Examples

To see what clang-uml can do, checkout the test cases documentation here.

In order to see diagrams for the clang-uml itself, based on its own config run the following:

make clanguml_diagrams

and checkout the SVG diagrams in docs/diagrams folder.

Class diagrams

Example

Source code:

template <typename T, typename P> struct A {
    T t;
    P p;
};

struct B {
    std::string value;
};

template <typename T> using AString = A<T, std::string>;
template <typename T> using AStringPtr = A<T, std::unique_ptr<std::string>>;

template <typename T>
using PairPairBA = std::pair<std::pair<B, A<long, T>>, long>;

template <class T> using VectorPtr = std::unique_ptr<std::vector<T>>;
template <class T> using APtr = std::unique_ptr<A<double, T>>;
template <class T> using ASharedPtr = std::shared_ptr<A<double, T>>;
template <class T, class U>
using AAPtr = std::unique_ptr<std::pair<A<double, T>, A<long, U>>>;

template <typename T> using SimpleCallback = std::function<void(T, int)>;
template <typename... T> using GenericCallback = std::function<void(T..., int)>;
using VoidCallback = GenericCallback<void *>;

using BVector = std::vector<B>;
using BVector2 = BVector;

using AIntString = AString<int>;
using ACharString = AString<char>;
using AWCharString = AString<wchar_t>;
using AStringString = AString<std::string>;
using BStringString = AStringString;

class R {
    PairPairBA<bool> bapair;

    APtr<bool> abool;
    AAPtr<bool, float> aboolfloat;
    ASharedPtr<float> afloat;
    A<bool, std::string> boolstring;
    AStringPtr<float> floatstring;
    AIntString intstring;
    AStringString stringstring;
    BStringString bstringstring;

protected:
    BVector bs;

public:
    BVector2 bs2;
    SimpleCallback<ACharString> cb;
    GenericCallback<AWCharString> gcb;
    VoidCallback vcb;
    VectorPtr<B> vps;
};

generates the following diagram (via PlantUML):

Open the raw image here, and checkout the hover tooltips and hyperlinks to classes and methods.

Sequence diagrams

Example

The following C++ code:

#include <algorithm>
#include <numeric>
#include <vector>

namespace clanguml {
namespace t20001 {

namespace detail {
struct C {
    auto add(int x, int y) { return x + y; }
};
}

class A {
public:
    A() {}

    int add(int x, int y) { return m_c.add(x, y); }

    int add3(int x, int y, int z)
    {
        std::vector<int> v;
        v.push_back(x);
        v.push_back(y);
        v.push_back(z);
        auto res = add(v[0], v[1]) + v[2];
        log_result(res);
        return res;
    }

    void log_result(int r) {}

private:
    detail::C m_c{};
};

class B {
public:
    B(A &a)
        : m_a{a}
    {
    }

    int wrap_add(int x, int y)
    {
        auto res = m_a.add(x, y);
        m_a.log_result(res);
        return res;
    }

    int wrap_add3(int x, int y, int z)
    {
        auto res = m_a.add3(x, y, z);
        m_a.log_result(res);
        return res;
    }

private:
    A &m_a;
};

int tmain()
{
    A a;
    B b(a);

    return b.wrap_add3(1, 2, 3);
}
}
}

generates the following diagram (via PlantUML):

Package diagrams

Example

The following C++ code:

namespace clanguml {
namespace t30003 {

namespace ns1 {
namespace ns2_v1_0_0 {
class A {
};
}

namespace [[deprecated]] ns2_v0_9_0 {
class A {
};
}

namespace {
class Anon final {
};
}
}

namespace [[deprecated]] ns3 {

namespace ns1::ns2 {
class Anon : public t30003::ns1::ns2_v1_0_0::A {
};
}

class B : public ns1::ns2::Anon {
};
}
}
}

generates the following diagram (via PlantUML):

Include diagrams

In case you're looking for a simpler tool to visualize and analyze include graphs checkout my other tool - clang-include-graph

Example

The following C++ code structure:

tests/t40001
├── include
│   ├── lib1
│   │   └── lib1.h
│   └── t40001_include1.h
└── src
    └── t40001.cc

generates the following diagram (via PlantUML) based on include directives in the code:

Default mappings

UML	PlantUML
Inheritance
Association
Dependency
Aggregation
Composition
Template specialization/instantiation
Nesting (inner class/enum)
Include (local)
Include (system)

Diagram content filtering

For typical code bases, generating a single diagram from entire code or even a single namespace can be too big to be useful, e.g. as part of documentation. clang-uml allows specifying content to be included and excluded from each diagram using simple YAML configuration:

include:
  # Include only elements from these namespaces
  namespaces:
    - clanguml::common
    - clanguml::config
  # Include all subclasses of ClassA (including ClassA)
  subclasses:
    - clanguml::common::ClassA
  # and specializations of template Class<T> (including Class<T>)
  specializations:
    - clanguml::common::ClassT<T>
  # and all classes depending on Class D
  dependants:
    - clanguml::common::ClassD
  # and all dependencies of ClassE
  dependencies:
    - clanguml::common::ClassE
  # and classes in direct relation to ClassB (including ClassB)
  context:
    - clanguml::common::ClassB
  # Include only inheritance relationships
  relationships:
    - inheritance
exclude:
  # Exclude all elements from detail namespace
  namespaces:
    - clanguml::common::detail
  # and also exclude ClassF
  elements:
    - clanguml::common::ClassF

Comment decorators

clang-uml provides a set of in-comment directives, called decorators, which allow custom control over generation of UML diagrams from C++ and overriding default inference rules for relationships.

The following decorators are currently supported:

• note - add a PlantUML note to a C++ entity
• skip - skip the underlying C++ entity
• skiprelationship - skip only relationship generation for a class property
• composition - document the property as composition
• association - document the property as association
• aggregation - document the property as aggregation
• style - add PlantUML style to a C++ entity

Doxygen integration

clang-uml decorstors can be omitted completely in Doxygen, by adding the following lines to the Doxygen config file:

ALIASES                += clanguml=""
ALIASES                += clanguml{1}=""
ALIASES                += clanguml{2}=""
ALIASES                += clanguml{3}=""

Test cases

The build-in test cases used for unit testing of the clang-uml, can be browsed here.

Acknowledgements

This project relies on the following great tools:

• Clang LibTooling - a C++ library for creating tools based on Clang
• PlantUML - language and diagram for generating UML diagrams
• Catch2 - C++ unit test framework
• glob - Unix style path expansion for C++
• CLI11 - command line parser for C++
• inja - a template engine for modern C++

Contributing

If you would like to contribute to the project, please checkout contributing guidelines.

LICENSE

Copyright 2021-present Bartek Kryza <bkryza@gmail.com>

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

  http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.