MISRA C:2004 rule 19.4 / extension

[Laessle]

In our code we want to use generic macros of kind

#define macro(a) int array[2] = {a, a};

unfortunately a do-while-zero loop does not helps, cause defined objects are only known within the loop.

So we would like to ask for a further exception of the described kind.

In the attachment you will find an example to demostrate the intention of such macros.
The program reads values of an Analog Digital Converter (via SPI) and writes modified values to a Pulswidth Generator (also via SPI).
All transfers are coded in an array (Transfer_List). The contents of the array depends on the hardware (baudrate, data-format) and the tranfer-typ (read, write
number of values). The C-file has no hardware dependant function. All hardware specific settings are encapsulated in the macro Create_Transfer_List.
Modifying the hardware only needs to modify the macro. Further I/Os can be implemented very easily.

We would appreciate your positve response.

Mit freundlichen Grüßen/Best regards,

Hans-Peter Lässle
Control Systems
ETC-D

Continental Teves AG & Co. oHG
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[misra-c]

This use of macros requires a deviation to be raised.

Where such use of macros creates clarity, its use is reasonable.

Unconstrained use of macros can create complex code which may lead to unexpected behaviour. This rule attempts to constrain the use of macros to simple contructs. Well designed use of complex macros is possible, and can be justified using a deviation. Examination of the post-processed code is recommended.

The use of macros will be reconsidered for MISRA-C3.