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From: Thiago Adams <thiago.adams@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: multi bytes character - how to make it defined behavior?
Date: Wed, 14 Aug 2024 15:28:10 -0300
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On 14/08/2024 15:12, Bart wrote:
> On 14/08/2024 18:40, Thiago Adams wrote:
>> On 14/08/2024 14:07, Bart wrote:
>
>>> That Chinese ideogram occupies 4 bytes. It is impossible for 'ab' to
>>> clash with some other Unicode character.
>>>
>>>
>>
>> My suggestion again. I am using string but imagine this working with
>> bytes from file.
>>
>>
>> #include <stdio.h>
>> #include <assert.h>
>
> ...
>> int get_value(const char* s0)
>> {
>> const char * s = s0;
>> int value = 0;
>> int uc;
>> s = utf8_decode(s, &uc);
>> while (s)
>> {
>> if (uc < 0x007F)
>> {
>> //multichar formula
>> value = value*256+uc;
>> }
>> else
>> {
>> //single char
>> value = uc;
>> break; //check if there is more then error..
>> }
>> s = utf8_decode(s, &uc);
>> }
>> return value;
>> }
>>
>> int main(){
>> printf("%d\n", get_value(u8"×"));
>> printf("%d\n", get_value(u8"ab"));
>> }
>
> I see your problem. You're mixing things up.
The objective is :
- make single characters have the Unicode value without having to use U''
- allow more than one chars like 'ab' in some cases where each
character is less than 0x007F. This can break code for instance '¼¼'.
but I am suspecting people are not using in this way (I hope)
> gcc will combine BYTE values together (by shifting by 8 bits or
> multiplying by 256), including the individual bytes that represent UTF8.
>
> You are combining ONLY ASCII bytes, and comparing the results with
> 21-bit Unicode values.
>
> That is meaningless. I'm not surprised you get a clash between A*256+B,
> and some arbitrary Unicode index.
>
In any case..my suggestion looks dangerous. But meanwhile this is not
well specified in the standard.