# V2642. MISRA. The '_Atomic' specifier should not be applied to the incomplete type 'void'.

This diagnostic rule is based on the MISRA (Motor Industry Software Reliability Association) software development guidelines.

This diagnostic rule is relevant only for C.

Applying a pointer to an incomplete atomic type (`_Atomic void *`) can lead to unexpected results and should be avoided.

In C, the `void *` type can be converted to any `T *` type (C11, 6.3.2.3.1). However, the standard does not impose any size and alignment requirements on the `_Atomic void *` pointer (C11, 6.2.5.28). As a result, converting between a pointer to (`_Atomic void *`) and a pointer to any arbitrary atomic type (`_Atomic T *`) may lead to undefined behavior.

The code example where the analyzer issues warnings:

    int _Atomic a;

    void main (void)
    {
      a = 5;
      void _Atomic * avp1 = &a;
      _Atomic(void)* avp2 = &a;
    }

This diagnostic is classified as:

MISRA-C-2023-11.10