C Code Quality Metrics

The program qmcalc will read a C source code file from its standard input and print on its standard output a single line containing tens of metrics regarding size, complexity, used keywords, comments and documentation, use of the C preprocessor, and observed formatting style. The full set of the metrics is documented in the file metrics.md.

The code has been written to run efficiently and reliably. The program receives the code to analyze from its standard input, so that it can process data coming e.g. directly out of a git show command, without having intermediate data touch the disk. Also, the program can process code that may not be easy (or possible) to fully parse using a compiler front-end, due e.g. to missing header files or an unknown compiler configuration.

Furthermore, the software is designed in a way that should allow its easy extension to other languages with C-like syntax, such as Java, C++, C#, and Go. The main thing you need to add is an XMetricsCalculator and an XKeyword class. Pull requests for such extensions are more than welcomed.

Building

Prerequisites

• C++ compiler
• GNU make
• CppUnit for running make test

To build type change the directory to src (cd src) and run make. This will also generate the files header.tab and header.txt, which can be used for loading the output into other programs for further processing.

Install

cd src && make install

Running

• The qmcalc program can process its standard input or report metrics on each of the specified files
• The qmcalc-showstyle wrapper takes as a single argument a directory, and reports the metrics for each C file in the directory
• The qmcalc-sumstyle wrapper takes as a single argument a directory, processes all C files in the directory, and for each metric from ncpp_directive and onward it reports
  • the metric's ordinal number,
  • the sum of the metric's values over all files, and
  • the percentage of files for which the metric is non-zero.

Further reading

The style checks performed are based on the following guidelines.

• Google
• FreeBSD
• GNU
• Recommended C Style and Coding Standards - updated version of the Indian Hill C Style and Coding Standards paper
• Wikipedia summary

Citation

• The tool is described in detail in the following paper. Diomidis Spinellis, Panos Louridas, and Maria Kechagia. The evolution of C programming practices: A study of the Unix operating system 1973–2015. In Willem Visser and Laurie Williams, editors, ICSE '16: Proceedings of the 38th International Conference on Software Engineering, pages 748–759, New York, May 2016. Association for Computing Machinery. (doi:10.1145/2884781.2884799)
• Some other metrics are based on the paper A Tale of Four Kernels.