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Re: Are char* and signed char* compatible (SCM_BYTEVECTOR_CONTENTS)?
From: |
Mike Gran |
Subject: |
Re: Are char* and signed char* compatible (SCM_BYTEVECTOR_CONTENTS)? |
Date: |
Fri, 26 Feb 2021 03:15:10 -0800 |
User-agent: |
Evolution 3.38.4 (3.38.4-1.fc33) |
On Fri, 2021-02-26 at 10:33 +0100, Vivien Kraus via General Guile
related discussions wrote:
> Hello,
>
> I’m trying to use a bytevector from C.
>
> 1. According to an example in the manual, SCM_BYTEVECTOR_CONTENTS can
> be assigned to a char*.
>
> 2. Also from the manual, it is a signed char*.
>
> 3. I've found this question online saying they are not compatible (
> https://stackoverflow.com/questions/12769500/why-is-char-not-compatible-with-signed-char-or-unsigned-char
> ).
>
> As I understand it, at least one of the above 3 affirmations is
> incorrect. Could someone clarify this to me?
Depending on your compiler and OS, char is either signed char (-128 to
127) or unsigned char (0 to 255). It is probably signed char.
You are free to cast the contents of a bytevector as signed char *,
unsigned char *, or char * (which is probably signed char). It depends
on what you want. When you use a bytevector from within Guile, it
will appear as unsigned 8=bit integers. But from within guile you could
use bytevector-s8-ref if you wanted to pull a byte out as a signed 8-
bit integer.
-Mike