Change the character encode in PostgreSQL C language function

Question

I am using PostgreSQL 9.5 64bit version on windows server. The character encoding of the database is set to UTF8.

I'd like to create a function that manipulates multibyte strings. (e.g. cleansing, replace etc.)

I copied C language logic for manipulating characters from a other system, The logic assumes that the character code is sjis.

I do not want to change C language logic, so I want to convert from UTF8 to sjis in C language function of Postgresql. Like the convert_to function. (However, since the convert_to function returns bytea type, I want to obtain it with TEXT type.)

Please tell me how to convert from UTF 8 to sjis in C language.

Create Function Script:

CREATE FUNCTION CLEANSING_STRING(character varying)
RETURNS character varying AS
'$libdir/MyFunc/CLEANSING_STRING.dll', 'CLEANSING_STRING'
LANGUAGE c VOLATILE STRICT;

C Source:

#include <stdio.h>
#include <string.h>
#include <postgres.h>
#include <port.h>
#include <fmgr.h>
#include <stdlib.h>
#include <builtins.h>

#ifdef PG_MODULE_MAGIC
PG_MODULE_MAGIC;
#endif

extern PGDLLEXPORT Datum CLEANSING_STRING(PG_FUNCTION_ARGS);

PG_FUNCTION_INFO_V1(CLEANSING_STRING);
Datum CLEANSING_STRING(PG_FUNCTION_ARGS)
{

    // Get Arg
    text *arg1 = (text *)PG_GETARG_TEXT_P(0);

    // Text to Char[]
    char *arg;
    arg = text_to_cstring(arg1);

    // UTF8 to Sjis
    //Char *sjisChar[] = foo(arg);  // something like that..

    // Copied from other system.(Assumes that the character code is sjis.)
    cleansingString(sjisChar);
    replaceStrimg(sjisChar);

    // Sjis to UTF8
    //arg = bar(sjisChar);  // something like that..

    //Char[] to Text and Return
    PG_RETURN_TEXT_P(cstring_to_text(arg));
}

See the functions any_to_server and server_to_any in src/backend/utils/mb/mbutils.c, and the comments at the top of mbutils.c — Craig Ringer
– Craig Ringer, Commented Nov 16, 2017 at 4:58
Thank you for your reply. I do not understand how to specify the third argument encoding. Is there a list of encoding somewhere? Is the usage correct? Char sjisChar[] = server_to_any(arg, strlen(arg), / sjis encoding number */ ); — Yuwaz
– Yuwaz, Commented Nov 16, 2017 at 5:50
sorry, pg_server_to_any and pg_any_to_server. And for the encoding name, see the pg_enc2name_tbl in src/backend/utils/mb/encnames.c and the pg_char_to_encoding function — Craig Ringer
– Craig Ringer, Commented Nov 16, 2017 at 6:23
@CraigRinger A program as expected was made! Thank you very much. The completed source will be described later as an answer. — Yuwaz
– Yuwaz, Commented Nov 16, 2017 at 13:02

Yuwaz · Accepted Answer · 2017-11-17 10:47:57Z

1

Succeeded in the way I was taught by question comments.

#include <mb/pg_wchar.h> //Add to include.

...

Datum CLEANSING_STRING(PG_FUNCTION_ARGS)
{

    // Get Arg
    text *arg1 = (text *)PG_GETARG_TEXT_P(0);

    // Text to Char[]
    char *arg;
    arg = text_to_cstring(arg1);

    // UTF8 to Sjis
    Char *sjisChar[] = pg_server_to_any(arg, strlen(arg), PG_SJIS);

    // Copied from other system.(Assumes that the character code is sjis.)
    cleansingString(sjisChar);
    replaceStrimg(sjisChar);

    // Sjis to UTF8
    arg =  pg_any_to_server(sjisChar, strlen(sjisChar), PG_SJIS); //It converts from SJIS to server (UTF 8), the third argument sets the encoding of the conversion source.

    //Char[] to Text and Return
    PG_RETURN_TEXT_P(cstring_to_text(arg));
}

answered Nov 17, 2017 at 10:47

Yuwaz

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