Converting Between Incompatible Types

Question

In some places in my code, I use the _mm_prefetch function, which takes in a const char * and int . The first parameter being the memory address of the object to prefetch. Since it's a const char * instead of void* , it needs to be cast.

Note: in the below context nextActive is a pointer to object.

Originally, I had:

_mm_prefetch( (const char *)this->nextActive, _MM_HINT_T1 );

This works fine; however, this leads to a warning, regarding C++ Core Guidelines Pro.safety: Type-safety profile Type.4.

I could use reinterpret_cast , but, that results in a warning violating Type 1a of the above ( Don't use reinterpret_cast )

Then, I thought, well, I can cast to void* then to const char* , but that results in a warning of Type 1d ( Don't cast between pointer types when the conversion could be implicit )

_mm_prefetch( static_cast<const char *>( static_cast<void *>( this->nextActive ) ), _MM_HINT_T1 );

Short of just suppressing the warnings when using _mm_prefetch , is there a proper way to covert between two incompatible types? Or are there always going to be warnings, because (of course) you probably shouldn't be casting between different types?

Answer 1

This should fix it:

void* ptr = this->nextActive;
_mm_prefetch(static_cast<const char*>(ptr), _MM_HINT_T1);

The only cast is from void* to const char* which is allowed.