MISRA C

MISRA C is a set of software development guidelines for the C programming language developed by MISRA (Motor Industry Software Reliability Association). Its aims are to facilitate code safety, security, portability and reliability in the context of embedded systems, specifically those systems programmed in ISO C / C90 / C99.

There is also a set of guidelines for MISRA C++ not covered by this article.

For the first two editions of MISRA-C (1998 and 2004) all Guidelines were considered as Rules. With the publication of MISRA C:2012 a new category of Guideline was introduced - the Directive whose compliance is more open to interpretation, or relates to process or procedural matters.

Although originally specifically targetted at the automotive industry, MISRA C has evolved as a widely accepted model for best practices by leading developers in sectors including automotive, aerospace, telecom, medical devices, defense, railway, and others. For example:

When a new software project is started, the latest MISRA standard should be used. Previous standards are still available for use with legacy software projects that need to refer to it.

Each Guideline is classified as Mandatory (new for MISRA C:2012), Required or Advisory. Furthermore, the MISRA Compliance document permits Advisory guidelines to be Disapplied

The rules can be divided logically into a number of categories:

MISRA C:2012 separately classifies each guideline as either Single Translation Unit or System.

MISRA C:2012 classifies the rules (but not the directives) as Decidable or Undecidable.

In April 2016, MISRA published MISRA Compliance:2016, which provides enhanced guidance on achieving compliance to MISRA C and MISRA C++.

In order for a piece of software to claim to be compliant to the MISRA C Guidelines, all mandatory rules shall be met and all required rules and directives shall either be met or subject to a formal deviation. Advisory rules may be disapplied without a formal deviation, but this should still be recorded in the project documentation.

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