Re: Simple string conversion from UCS2 to ISO8859-1

Il 21/02/2025 13:05, Richard Damon ha scritto:

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

I want to write a simple function that converts UCS2 string into ISO8859-1:
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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.

Sure, but this isn't an issue here.

I know I can use iconv() feature, but I'm on an embedded platform without an OS and without iconv() function.
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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.

Yes, but as a first approximation, 0x27 is much better than '?' for u2019.

Is there a simplified mapping table that can be written with if/switch?
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if (code < 0x80) {
   *dst++ = (char)code;
} else {
   switch (code) {
     case 0x2019: *dst++ = 0x27; break;  // Apostrophe
     case 0x...: *dst++ = ...; break;
     default: *ds++ = ' ';
   }
}
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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.

Yes, I have to decide, but it is a very big problem (there are thousands of Unicode symbols that can be approximated to another ISO8859-1 code). I'm wondering if such an approximation is just implemented somewhere.
For example, what iconv() does in this case?