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Analysis of C++ projects based on JSON …
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Contents

Analysis of C++ projects based on JSON Compilation Database

Jan 20 2022

General information

One of the ways to represent the structure of a C++ project is the JSON Compilation Database format. It's a file that contains the compilation parameters necessary to create object files from the source code of a project. Usually, the file has the name 'compile_commands.json'. A compilation database in JSON-format consists of an array of "command objects", where each command object specifies one way a translation unit is compiled in the project.

You can use the 'compile_commands.json' file to compile a project or analyze the project by third-party utilities. The PVS-Studio C and C++ analyzer works with this format as well.

Running the analysis and getting the report

To analyze the project on Linux and macOS, you need to use 'pvs-studio-analyzer' utility. To analyze the project on Windows, use 'CompileCommandsAnalyzer.exe' utility. The utility is usually located in the 'C:\Program Files (x86)\PVS-Studio' folder.

Analyze_Cpp_Projects_with_JSON_Compilation_DB/image1.png

To start the analysis and get the report, you need to run two commands.

The command example for Linux and macOS:

pvs-studio-analyzer analyze -f path_to_compile_commands.json \
    -l path_to_PVS-Studio.lic -o pvs.log -e excludepath -j<N>

plog-converter -a GA:1,2 -t tasklist -o project.tasks pvs.log

The command example for Windows:

CompilerCommandsAnalyzer.exe analyze -l path_to_PVS-Studio.lic ^
    -f path_to_compile_commands.json -o pvs.log -e exclude-path -j<N>

PlogConverter.exe -a GA:1,2 -t Plog -o analysis_report.plog pvs.log

If you run the analysis from the directory with the 'compile_commands.json' file, you may disable the '-f' flag.

To exclude directories with third-party libraries and/or tests from the analysis, you can use the '-e' flag. If there are several paths, it's necessary to write the '-e' flag for each path:

-e third-party -e tests

The analysis can be parallelized into multiple threads with the help of '-j' flag.

More detailed instructions for utilities on Linux/macOS and Windows are available here and here.

How to generate compile_commands.json

If by default the project does not contain 'compile_commands.json', you can choose one of the ways to generate such a file.

CMake project

To generate 'compile_commands.json, add one flag to the CMake call:

cmake -DCMAKE_EXPORT_COMPILE_COMMANDS=On .

It's possible to create the 'compile_commands.json' file only if the generator supports the JSON format. For example, such generators are Makefile and Ninja:

cmake -DCMAKE_EXPORT_COMPILE_COMMANDS=On -G Ninja .
cmake -DCMAKE_EXPORT_COMPILE_COMMANDS=On -G "NMake Makefiles" .

To use the Ninja generator for Windows, it is often required to execute commands from the Visual Studio developer's command line (e.g., 'x64 Native Tools Command Prompt for VS', etc.).

Ninja project

If the project is built directly with Ninja and there is a 'build.ninja' file in the project folder, use the following command to generate 'compile_commands.json':

ninja -t compdb > compile_command.json

QBS project

To generate 'compile_commands.json' in a project that use Qt Build System, execute the following command:

qbs generate --generator clangdb

Text Toolkit utility

Having trouble getting the 'compile_commands.json' file using GNU make? Try Text Toolkit. You can generate a compilation database either using the Web interface (only for Linux and macOS), or by launching a Python script. To generate a database online, take the following steps:

  • run the command 'make -nwi > output.txt';
  • copy the contents of the 'output.txt ' file and paste them to the window on the Text Toolkit website;
  • click the 'Generate' button to generate the compilation database in JSON format;
  • copy the obtained commands to the 'compile_commands.json' file.

To generate the 'compile_commands.json' using Python, you need to clone a repository from GitHub and run the following command:

ninja -nv | python path_to_texttoolkit_dir\cdg.py

Note: our repository is a fork of the original Text Toolkit's repository. We improved it and now it allows you to generate 'compile_commands.json' on Windows with the use of Ninja.

Bear utility (only for Linux and macOS)

The Bear (version 2.4 or higher) utility collects compilation parameters by intercepting the compiler calls during project build. To generate 'compile_commands.json', run the following command

bear -- <build_command>

The 'build_command' can be any build command such as 'make all' or './build.sh'.

intercept-build utility (only for Linux and macOS)

The 'intercept-build' utility in scan-build is similar to the Bear utility. The command to generate 'compile_commands.json':

intercept-build <build_command>

Compilation Database Generator utility (only for Linux and macOS)

Compile Database Generator (compiledb) is a utility that generates compilation databases for Makefile-based build systems. The example of the 'compile_commands.json' generation:

compiledb -n make

The '-n' flag means that the build won't happen (dry run).

Xcode project (macOS only)

With the xcpretty utility, you can generate 'compile_commands.json'. To do this, run the following command:

xcodebuild [flags] | xcpretty -r json-compilation-database

qmake project

To generate 'compile_commands.json' in the project that uses qmake, you can use IDE QtCreator version 4.8 or higher. Open the desired project and select 'Build->Generate Compilation Database for %project_name%' in the menu bar:

Analyze_Cpp_Projects_with_JSON_Compilation_DB/image2.png

The generated 'compile_commands.json' file will be in the project's build directory.

Note: this method of obtaining 'compile_commands.json' does not have automation. We recommend to use this method only to evaluate the analyzer.

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