Why is the MISRA-C:2012 directive D4.10 raised on #pragma once?

The MISRA-C:2012 directive 4.10 says that "Precautions shall be taken in order to prevent the contents of a header file being included more than once."

In C it is possible to prevent header file to be included more than once thanks to the pragma #pragma once.

But Polyspace will raise a violation of D4.10 on this pragma. Why?

Answer 1

[MathWorks Support Team]

The #pragma once directive, even if supported by most of the compilers, is not part of the C standard.

It is then “implementation-defined”, and in some corner cases, where copied include files or include files with same name are in different include directories, it can lead to unintended behavior.

The MISRA-C:2012 standard does not list this pragma in the description of the directive D4.10.

The two forms given in the standard are:

#if !defined ( identifier )

#define identifier

...

#endif

and

#ifndef identifier

#define identifier

...

#endif

Polyspace follows the MISRA-C:2012 standard and does not consider #pragma once as a valid include guard.