With std::byte standardized, when do we use a void* and when a byte*?

Question

C++17 will include std::byte, a type for one atomically-addressable unit of memory, having 8 bits on typical computers.

Before this standardization, there is already a b

Answer 1

(This is a potential rule of thumb which comes off the top of my head, not condoned by anyone.)

Rule of thumb: When to use which kind of pointer?

• Use char * for sequences of textual characters, not anything else.
• Use void * in type-erasure scenarios, i.e. when the pointed-to data is typed, but for some reason a typed pointer must not be used or it cannot be determined whether it's typed or not.
• Use byte * for raw memory for which there is no indication of it holding any typed data.

An exception to the above:

• Also use void */unsigned char */char * when older or non-C++ forces you and you would otherwise use byte * - but wrap that with a byte *-based interface as tightly as you can rather than exposing it to the rest of your C++ code.

Examples

void * my_custom_malloc(size_t size) - wrong
byte * my_custom_malloc(size_t size) - right

struct buffer_t { byte* data; size_t length; my_type_t data_type; } - wrong
struct buffer_t { void* data; size_t length; my_type_t data_type; } - right