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Date: Tue, 30 Jan 2024 13:56:22 +0300
From: Oleg Tselebrovskiy <o.tselebrovskiy@postgrespro.ru>
To: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Cc: pgsql-hackers@postgresql.org
Subject: Re: Returning non-terminated string in ECPG Informix-compatible
 function
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Here's the code for bug reproduction:
#include <stdio.h>
#include <stdlib.h>

EXEC SQL INCLUDE pgtypes_interval.h;
EXEC SQL INCLUDE ecpg_informix.h;

EXEC SQL BEGIN DECLARE SECTION;
	char dirty_str[100] = "aaaaaaaaa_bbbbbbbb_ccccccccc_ddddddddd_";
	interval *interval_ptr;
EXEC SQL END DECLARE SECTION;

int main()
{
	interval_ptr = (interval *) malloc(sizeof(interval));
	interval_ptr->time = 100000000;
	interval_ptr->month = 240;

	printf("dirty_str contents before intoasc: %s\n", dirty_str);
	intoasc(interval_ptr, dirty_str);
	printf("dirty_str contents after intoasc: %s\n", dirty_str);
	return 0;
}

And here's the output:

dirty_str contents before intoasc: 
aaaaaaaaa_bbbbbbbb_ccccccccc_ddddddddd_
dirty_str contents after intoasc: @ 20 years 1 min 40 
secscccc_ddddddddd_

I compiled it with following commands (provided for quicker 
reproduction):
/path/to/pgsql/bin/ecpg informix_bug_example.pgc
gcc -I/path/to/pgsql/include -c informix_bug_example.c
gcc -o informix_bug_example informix_bug_example.o -L/path/to/pgsql/lib 
-lecpg -lecpg_compat

I've also found at least one project that uses intoasc() in it - 
https://github.com/credativ/informix_fdw/

Oleg Tselebrovskiy, Postgres Pro