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Message-ID: <7104a7370510211630s294123f6te3465b593c5e32a9@mail.gmail.com>
Date: Sat, 22 Oct 2005 02:30:02 +0300
From: Volkan YAZICI <volkan.yazici@gmail.com>
To: =?ISO-8859-1?Q?Jochen_Kokem=FCller?= <jochen@kokemueller.de>
Subject: Re: Reading bytea field
Cc: pgsql-interfaces@postgresql.org
In-Reply-To: <43593798.5060707@kokemueller.de>
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References: <43593798.5060707@kokemueller.de>

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Hi,

On 10/21/05, Jochen Kokem=FCller <jochen@kokemueller.de> wrote:
> I read that it is better to use PQexecParams instead of PQescape. In the
> bytea field is then the picture with every Byte escaped. So the first
> few bytes look like this:
>
>  \377\330\377\340\000\020JFIF ...
>
> I wouldn't bother if i knew how to unescape this sequence. I supposed
> that this is more or less an internal representation, but when i try to
> retrieve the data. i get it like this.

If you'd use PQexecParams() for SELECT query with resultType =3D 1, you
shouldn't have any problem. Take a look at the examples in the
attachment.

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#include <stdio.h>
#include <stdlib.h>

#include <libpq-fe.h>

#define MAX_BUF_SZ	8192

void
exit_nicely(PGconn *conn)
{
	PQfinish(conn);
	exit(1);
}

int
main(void)
{
	PGconn		*conn;
	PGresult	*res;
	const char	 fname[] = "newimage.jpg";
	FILE		*fp;
	char		*s;
	int			 len;

	conn = PQconnectdb("dbname=test");
	if (PQstatus(conn) != CONNECTION_OK)
	{
		fprintf(stderr, "Error: PQconnectdb: %s", PQerrorMessage(conn));
		exit_nicely(conn);
	}

	res = PQexecParams(conn, "SELECT data FROM file_arch LIMIT 1",
					   0, NULL, NULL, NULL, NULL, 1);
	if (PQresultStatus(res) != PGRES_TUPLES_OK)
	{
		fprintf(stderr, "Error: PQexecParams: %s", PQerrorMessage(conn));
		PQclear(res);
		exit_nicely(conn);
	}

	fp = fopen(fname, "w");
	if (!fp)
	{
		perror("fopen");
		PQclear(res);
		exit_nicely(conn);
	}

	len = PQgetlength(res, 0, 0);
	s = PQgetvalue(res, 0, 0);
	fwrite(s, sizeof(char), len, fp);
	
	fclose(fp);
	PQclear(res);
	PQfinish(conn);

	return 0;
}

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#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>

#include <libpq-fe.h>

void
exit_nicely(PGconn *conn)
{
	PQfinish(conn);
	exit(1);
}

int
main(void)
{
	const char		fname[] = "image.jpg";
	FILE			*fp;
	PGconn			*conn;
	PGresult		*res;
	struct	stat	 st;
	char			*buf;
	const int		 l = 1;
	const char		*param_vals[l];
	int				 param_lens[l];
	int				 param_fmts[l];

	conn = PQconnectdb("dbname=test");
	if (PQstatus(conn) != CONNECTION_OK)
	{
		fprintf(stderr, "Error: PQconnectdb: %s", PQerrorMessage(conn));
		exit_nicely(conn);
	}

	if(stat(fname, &st) < 0)
	{
		perror("stat");
		exit_nicely(conn);
	}
	
	buf = malloc(st.st_size);
	if (!buf)
	{
		perror("malloc");
		exit_nicely(conn);
	}

	fp = fopen("image.jpg", "r");
	if (!fp)
	{
		free(buf);
		perror("fopen");
		exit_nicely(conn);
	}
	fread(buf, sizeof(char), st.st_size, fp);
	fclose(fp);

	param_vals[0] = buf;
	param_lens[0] = st.st_size;
	param_fmts[0] = 1;
	res = PQexecParams(conn, "INSERT INTO file_arch (data) VALUES ($1)",
					   l, NULL, param_vals, (const int *) param_lens,
					   (const int *) param_fmts, 1);
	if (PQresultStatus(res) != PGRES_COMMAND_OK)
	{
		fprintf(stderr, "INSERT failed: %s", PQerrorMessage(conn));
		PQclear(res);
		free(buf);
		exit_nicely(conn);
	}
	
	PQclear(res);
	free(buf);

	return 0;
}

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