Is cast from uint8_t* to char* acceptable

Question

Concerning this question

Convert from uint8_t * to char * in C

The suggestion was simply to cast with (char*). Why is this acceptable in this context? Or did the responder just take the question literally?

Casting unsigned (depending on the implementation) to signed feels dubious.

Answer 1

In C, it is allowed to access a variable of a given type through a pointer to the signed or unsigned version of that that type.

This is specified in section 6.5p7 of the C standard:

An object shall have its stored value accessed only by an lvalue expression that has one of the following types:

• a type compatible with the effective type of the object,
• a qualified version of a type compatible with the effective type of the object,
• a type that is the signed or unsigned type corresponding to the effective type of the object,
• a type that is the signed or unsigned type corresponding to a qualified version of the effective type of the object,
• an aggregate or union type that includes one of the aforementioned types among its members (including, recursively, a member of a subaggregate or contained union), or
• a character type.

A uint8_t is an alias for an unsigned char (at least, on systems where CHAR_BIT is 8), so it is allowed to convert an uint8_t * to a char * and subsequently dereference the resulting pointer.

Note also that, per the last bullet point above, using a pointer any character type is allowed to access any kind of object.