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Re: [Bug-readline] rl_point, multibyte strings, and the cursor position

From: Chet Ramey
Subject: Re: [Bug-readline] rl_point, multibyte strings, and the cursor position
Date: Tue, 17 Feb 2015 11:44:41 -0500
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:31.0) Gecko/20100101 Thunderbird/31.4.0

On 2/16/15 4:52 PM, Ulf Magnusson wrote:
> On Mon, Feb 16, 2015 at 4:43 PM, Ulf Magnusson <address@hidden> wrote:
>> I'll try it. Thanks for the suggestion!
>> /Ulf
> Here's what I came up with in case someone else runs into the same
> problem. I'm sure there's more stuff to handle (not sure what to do
> for non-printable characters for example), but it seems to handle
> multibyte (tested using åäö's and Chinese) and combining characters
> correctly for UTF-8 at least:

This is basically what an implementation of wcswidth looks like.  A couple
of suggestions:

> // Returns the total width (in columns) of the characters in the 'n'-byte
> // prefix of the null-terminated multibyte string 's'. If 'n' is larger than
> // 's', returns the total width of the string. Suitable for calculating a
> // cursor position.
> //
> // Makes a guess for malformed strings.
> static size_t strnwidth(const char *s, size_t n) {
>     mbstate_t shift_state;
>     wchar_t wc;
>     size_t wc_len;
>     size_t width = 0;
>     // Start in the initial shift state.
>     memset(&shift_state, '\0', sizeof shift_state);
>     for (size_t i = 0; i < n; i += wc_len) {
>         // Extract the next multibyte character.
>         wc_len = mbrtowc(&wc, s + i, MB_CUR_MAX, &shift_state);
>         if (wc_len == 0)
>             // Reached the end of the string.
>             break;
>         if (wc_len == -1)

wc_len is a size_t, which is usually unsigned.  You need to cast the -1
to (size_t)-1.  You also need to handle mbrtowc returning (size_t)-2.

``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU    address@hidden    http://cnswww.cns.cwru.edu/~chet/

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