Re: Simple string conversion from UCS2 to ISO8859-1

On 2/21/25 6:40 AM, pozz wrote:

I want to write a simple function that converts UCS2 string into ISO8859-1:
 void ucs2_to_iso8859p1(char *ucs2, size_t size);
 ucs2 is a string of type "00480065006C006C006F" for "Hello". I'm passing size because ucs2 isn't null terminated.

Typically UCS2 strings ARE null terminated, it just a null is two bytes long.

 I know I can use iconv() feature, but I'm on an embedded platform without an OS and without iconv() function.
 It is trivial to convert "0000"-"007F" chars: it's a simple cast from unsigned int to char.

Note, I think you will find that it is that 0000-00FF that match. (as I remember ISO8859-1 was the base for starting Unicode).

 It isn't so simple to convert higher codes. For example, the small e with grave "00E8" can be converted to 0xE8 in ISO8859-1, so it's trivial again. But I saw the code "2019" (apostrophe) that can be rendered as 0x27 in ISO8859-1.

To be correct, u2019 isn't 0x27, its just character that looks a lot like it.

 Is there a simplified mapping table that can be written with if/switch?
 if (code < 0x80) {
   *dst++ = (char)code;
} else {
   switch (code) {
     case 0x2019: *dst++ = 0x27; break;  // Apostrophe
     case 0x...: *dst++ = ...; break;
     default: *ds++ = ' ';
   }
}
 I'm not searching a very detailed and correct mapping, but just a "sufficient" implementation.
 

Then you have to decide which are sufficient mappings. No character above FF *IS* the character below, but some have a close approximation, so you will need to decide what to map.