Thanks Clemens. You’re right about changing the UTF8String* to char* as it now
works but when trying it with a column containing Unicode characters it didn’t.
I’d have liked to have tried it with windows wchar_t* type but If I try using
if (sqlite3_create_collation16(SQLiteDB, "Compare", SQLITE_UTF16,
NULL, &Compare) != SQLITE_OK)
throw Exception("Collation creation error");
I get the message “no such collation sequence: Compare” when running the query.
From: Clemens Ladisch<mailto:clem...@ladisch.de>
Sent: 01 February 2017 17:32
To:
sqlite-users@mailinglists.sqlite.org<mailto:sqlite-users@mailinglists.sqlite.org>
Subject: Re: [sqlite] Help with custom collation
x wrote:
> int Compare(void* Data, int Len1, const void *s1, int Len2, const void *s2)
> {
> const UTF8String *S1 = static_cast<const UTF8String*>(s1),
> *S2 = static_cast<const UTF8String*>(s2);
> return 0;
> }
>
> if (sqlite3_create_collation(SQLiteDB, "Compare", SQLITE_UTF8, NULL,
> &Compare) != SQLITE_OK)
> throw Exception("Collation creation error");
>
> S1 and S2 appear to point to NULL values.
What is "UTF8String"? If it is anything different from "char", the code is
wrong.
> If I change the select to ‘select ID from IDTbl order by ID collate Compare’
> the Compare function is never entered.
> Is this because ID is an integer column?
No, it is because the values in that column are integer values.
> Is there no way to implement a custom collation on an integer column?
There is no way to implement a custom collation for integer values.
Collations are used only for string values.
Regards,
Clemens
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