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How to resolve MISRA C:2012 error regarding to memcpy function?

I am using standard memcpy function which declared in string.h file thus:

extern void *   memcpy(void *, const void *, size_t);

Case 1 : My code is compiled without any error or warnings. 

const uint8_t *buff = (uint8_t*)Getbuff();
uint8_t data[3] = {0};
memcpy((void*)data,(const void*)(buff+2),3U);

After checking MISRA C:2012 I am getting following MISRA error:

performing pointer arithmetic via addition [MISRA 2012 Rule 18.4, advisory] memcpy((void*)data,(const void*)(buff+2),3U);

Case 2 : If I fix MISRA error in Case 1 thus:

const uint8_t *buff = (uint8_t*)Getbuff();
uint8_t data[3] = {0};
memcpy((void*)data,(const void*)(buff[2]),3U);

I am getting compile time warning and a different MISRA error.

Compile time warning : 

cast to pointer from integer of different size

MISRA error:

explicit cast from 'const UINT8' (aka 'const unsigned char') to 'const void *' [MISRA 2012 Rule 11.6, required]memcpy((void*)data,(const void*)(buffer[2]),3U);

Solution

  • Just;

    memcpy( data, &buff[2], 3u ) ;

    Both the pointer arithmetic and casts are unnecessary and contrary to MISRA rules.

    To cast to a void* rather misunderstands the purpose of a void-pointer, and casting in general can suppress essential warnings that the compiler might otherwise issue. The resulting de-clutter makes the code much easier to read and MISRA compliant.

    Your second case was also semantically incorrect, and would not have resulted in correct behaviour - warnings are not always just warnings; often they indicate semantic errors. For the compiler "error" just means "cannot be compiled" (syntactic error); a semantic error is one where the code does not do what was intended.