The linked-to essay points out that char is only "at least 8 bits", and links to https://cppreference.com/c/language/arithmetic_types which confirms that point.

https://smd.hu/Data/Analog/DSP/SHARC/C&C++%20Compiler%20&%20... says the cc21k compiler for ADSP-21xxx DSP systems has char as 32 bits signed, and that the compiler handles ANSI/ISO standard C.

So I don't believe your statement "sizeof(char) is guaranteed to always be 1" is correct.

> chars are also how you access the byte-level representation of objects in C

Where does the spec say that a char can be used to address any point in an object?

There's all sorts of oddities like tagged architectures which the C spec handles which I know essentially nothing about, but which break common expectations about how C works. I believe this is one of them.

I believe the following is undefined behavior in C, even though your compiler may let you do it, at least sometimes, and on modern desktop hardware:

  int i = 12345;
  char *s = ((char *)&i) + 1;
  char c = *s;

  char tmp[sizeof(int)];
  memcpy(tmp, &i, sizeof(int));
  char c = tmp[1];

> The linked-to essay points out that char is only "at least 8 bits", and links to https://cppreference.com/c/language/arithmetic_types which confirms that point.

Yes, but in C standardese a "byte" is not necessarily the 8 bits that it's normally thought to be these days. From C89 Section 2.2.4.2 Numerical Limits [-1]:

> maximum number of bits for smallest object that is not a bit-field (byte) CHAR_BIT 8

i.e., CHAR_BIT is the number of bits in a byte. C23 has a similar definition, and further defines CHAR_WIDTH that is defined to expand to the same value as CHAR_BIT.

> So I don't believe your statement "sizeof(char) is guaranteed to always be 1" is correct.

From C89 section 3.3.3.4 The sizeof operator [0]:

> When applied to an operand that has type char, unsigned char, or signed char, (or a qualified version thereof) the result is 1.

This wording remains basically identical through C23 [1].

> Where does the spec say that a char* can be used to address any point in an object?

From C89 section 3.3 Expressions:

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

> <snip>

> * a character type.

This also remains the case up through C23.

I think you're thinking of the strict aliasing rule with your example, but character types are one of the exceptions to said rule so I think your example is actually fully defined. It'd be UB if you casted to an incompatible type like a float, I believe.

[-1]: https://port70.net/%7Ensz/c/c89/c89-draft.html#2.2.4.2

[0]: https://port70.net/%7Ensz/c/c89/c89-draft.html#3.3.3.4

[1]: https://port70.net/%7Ensz/c/c23/n3220.html#6.5.4.4

[2]: https://port70.net/%7Ensz/c/c89/c89-draft.html#3.3

[3]: https://port70.net/%7Ensz/c/c23/n3220.html#6.5.1