PostgreSQL数据库学习手册之libpq-C库的例子程序

　　 
　　1.14. 例子程序

Example 1-1. libpq 例子程序 1
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/*
* testlibpq.c
*
* Test the C version of libpq, thePostgreSQLfrontend
* library.
* 测试 PostgreSQL 前端库 libpq 的 C 版本

*/
#include <stdio.h>
#include <libpq-fe.h>

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

main()
{
char *pghost,
*pgport,
*pgoptions,
*pgtty;
char *dbName;
int nFields;
int i,
j;

/* FILE *debug; */

PGconn *conn;
PGresult *res;

/*
* begin, by setting the parameters for a backend connection if the
* parameters are null, then the system will try to use reasonable
* defaults by looking up environment variables or, failing that,
* using hardwired constants
*/
pghost = NULL; /* host name of the backend server */
pgport = NULL; /* port of the backend server */
pgoptions = NULL; /* special options to start up the backend
* server */
pgtty = NULL; /* debugging tty for the backend server */
dbName = "template1";

/* make a connection to the database */
conn = PQsetdb(pghost, pgport, pgoptions, pgtty, dbName);

/*
* check to see that the backend connection was suclearcase/" target="_blank" >ccessfully made
*/
if (PQstatus(conn) == CONNECTION_BAD)
{
fprintf(stderr, "Connection to database '%s' failed.\n", dbName);
fprintf(stderr, "%s", PQerrorMessage(conn));
exit_nicely(conn);
}

/* debug = fopen("/tmp/trace.out","w"); */
/* PQtrace(conn, debug); */

/* start a transaction block */
res = PQexec(conn, "BEGIN");
if (!res || PQresultStatus(res) != PGRES_COMMAND_OK)
{
fprintf(stderr, "BEGIN command failed\n");
PQclear(res);
exit_nicely(conn);
}

/*
* should PQclear PGresult whenever it is no longer needed to avoid
* memory leaks
*/
PQclear(res);

/*
* fetch rows from the pg_database, the system catalog of
* databases
*/
res = PQexec(conn, "DECLARE mycursor CURSOR FOR SELECT * FROM pg_database");
if (!res || PQresultStatus(res) != PGRES_COMMAND_OK)
{
fprintf(stderr, "DECLARE CURSOR command failed\n");
PQclear(res);
exit_nicely(conn);
}
PQclear(res);
res = PQexec(conn, "FETCH ALL in mycursor");
if (!res || PQresultStatus(res) != PGRES_TUPLES_OK)
{
fprintf(stderr, "FETCH ALL command didn't return tuples properly\n");
PQclear(res);
exit_nicely(conn);
}

/* first, print out the attribute names */
nFields = PQnfields(res);
for (i = 0; i < nFields; i++)
printf("%-15s", PQfname(res, i));
printf("\n\n");

/* next, print out the rows */
for (i = 0; i < PQntuples(res); i++)
{
for (j = 0; j < nFields; j++)
printf("%-15s", PQgetvalue(res, i, j));
printf("\n");
}
PQclear(res);

/* close the cursor */
res = PQexec(conn, "CLOSE mycursor");
PQclear(res);

/* commit the transaction */
res = PQexec(conn, "COMMIT");
PQclear(res);

/* close the connection to the database and cleanup */
PQfinish(conn);

/* fclose(debug); */
return 0;

}
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Example 1-2. libpq 例子程序 2


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/*
* testlibpq2.c
* 测试异步通知接口
*
* 运行此程序，然后从另外一个窗口的 psql 里运行 NOTIFY TBL2;
*
* 或者，如果你想好玩一点，尝试下面动作∶
* 用下面的语句填充一个数据库∶
*
* CREATE TABLE TBL1 (i int4);
*
* CREATE TABLE TBL2 (i int4);
*
* CREATE RULE r1 AS ON INSERT TO TBL1 DO
* (INSERT INTO TBL2 values (new.i); NOTIFY TBL2);
*
* 然后∶
*
* INSERT INTO TBL1 values (10);
*
*/
#include <stdio.h>
#include "libpq-fe.h"

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

main()
{
char *pghost,
*pgport,
*pgoptions,
*pgtty;
char *dbName;
int nFields;
int i,
j;

PGconn *conn;
PGresult *res;
PGnotify *notify;

/*
* begin, by setting the parameters for a backend connection if the
* parameters are null, then the system will try to use reasonable
* defaults by looking up environment variables or, failing that,
* using hardwired constants
*/
pghost = NULL; /* host name of the backend server */
pgport = NULL; /* port of the backend server */
pgoptions = NULL; /* special options to start up the backend
* server */
pgtty = NULL; /* debugging tty for the backend server */
dbName = getenv("USER"); /* change this to the name of your test
* database */

/* make a connection to the database */
conn = PQsetdb(pghost, pgport, pgoptions, pgtty, dbName);

/*
* check to see that the backend connection was successfully made
*/
if (PQstatus(conn) == CONNECTION_BAD)
{
fprintf(stderr, "Connection to database '%s' failed.\n", dbName);
fprintf(stderr, "%s", PQerrorMessage(conn));
exit_nicely(conn);
}

res = PQexec(conn, "LISTEN TBL2");
if (!res || PQresultStatus(res) != PGRES_COMMAND_OK)
{
fprintf(stderr, "LISTEN command failed\n");
PQclear(res);
exit_nicely(conn);
}

/*
* should PQclear PGresult whenever it is no longer needed to avoid
* memory leaks
*/
PQclear(res);

while (1)
{

/*
* wait a little bit between checks; waiting with select()
* would be more efficient.
*/
sleep(1);
/* collect any asynchronous backend messages */
PQconsumeInput(conn);
/* check for asynchronous notify messages */
while ((notify = PQnotifies(conn)) != NULL)
{
fprintf(stderr,
"ASYNC NOTIFY of '%s' from backend pid '%d' received\n",
notify->relname, notify->be_pid);
free(notify);
}
}

/* close the connection to the database and cleanup */
PQfinish(conn);

return 0;
}

Example 1-3. libpq 例子程序 3

/*
* testlibpq3.c 测试 C 版本的 Libpq --PostgreSQL的前端库．
* 测试二进制游标接口
*
*
*
* 用下面语句填充一个数据库∶
*
* CREATE TABLE test1 (i int4, d real, p polygon);
*
* INSERT INTO test1 values (1, 3.567, polygon '(3.0, 4.0, 1.0, 2.0)');
*
* INSERT INTO test1 values (2, 89.05, polygon '(4.0, 3.0, 2.0, 1.0)');
*
* 预期的输出是∶
*
* tuple 0: got i = (4 bytes) 1, d = (4 bytes) 3.567000, p = (4
* bytes) 2 points boundbox = (hi=3.000000/4.000000, lo =
* 1.000000,2.000000) tuple 1: got i = (4 bytes) 2, d = (4 bytes)
* 89.050003, p = (4 bytes) 2 points boundbox =
* (hi=4.000000/3.000000, lo = 2.000000,1.000000)
*
*
*/
#include <stdio.h>
#include "libpq-fe.h"
#include "utils/geo_decls.h" /* for the POLYGON type */

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

main()
{
char *pghost,
*pgport,
*pgoptions,
*pgtty;
char *dbName;
int nFields;
int i,
j;
int i_fnum,
d_fnum,
p_fnum;
PGconn *conn;
PGresult *res;

/*
* begin, by setting the parameters for a backend connection if the
* parameters are null, then the system will try to use reasonable
* defaults by looking up environment variables or, failing that,
* using hardwired constants
*/
pghost = NULL; /* host name of the backend server */
pgport = NULL; /* port of the backend server */
pgoptions = NULL; /* special options to start up the backend
* server */
pgtty = NULL; /* debugging tty for the backend server */

dbName = getenv("USER"); /* change this to the name of your test
* database */

/* make a connection to the database */
conn = PQsetdb(pghost, pgport, pgoptions, pgtty, dbName);

/*
* check to see that the backend connection was successfully made
*/
if (PQstatus(conn) == CONNECTION_BAD)
{
fprintf(stderr, "Connection to database '%s' failed.\n", dbName);
fprintf(stderr, "%s", PQerrorMessage(conn));
exit_nicely(conn);
}

/* start a transaction block */
res = PQexec(conn, "BEGIN");
if (!res || PQresultStatus(res) != PGRES_COMMAND_OK)
{
fprintf(stderr, "BEGIN command failed\n");
PQclear(res);
exit_nicely(conn);
}

/*
* should PQclear PGresult whenever it is no longer needed to avoid
* memory leaks
*/
PQclear(res);

/*
* fetch rows from the pg_database, the system catalog of
* databases
*/
res = PQexec(conn, "DECLARE mycursor BINARY CURSOR FOR SELECT * FROM test1");
if (!res || PQresultStatus(res) != PGRES_COMMAND_OK)
{
fprintf(stderr, "DECLARE CURSOR command failed\n");
PQclear(res);
exit_nicely(conn);
}
PQclear(res);

res = PQexec(conn, "FETCH ALL in mycursor");
if (!res || PQresultStatus(res) != PGRES_TUPLES_OK)
{
fprintf(stderr, "FETCH ALL command didn't return tuples properly\n");
PQclear(res);
exit_nicely(conn);
}

i_fnum = PQfnumber(res, "i");
d_fnum = PQfnumber(res, "d");
p_fnum = PQfnumber(res, "p");

for (i = 0; i < 3; i++)
{
printf("type[%d] = %d, size[%d] = %d\n",
i, PQftype(res, i),
i, PQfsize(res, i));
}
for (i = 0; i < PQntuples(res); i++)
{
int *ival;
float *dval;
int plen;
POLYGON *pval;

/* we hard-wire this to the 3 fields we know about */
ival = (int *) PQgetvalue(res, i, i_fnum);
dval = (float *) PQgetvalue(res, i, d_fnum);
plen = PQgetlength(res, i, p_fnum);

/*
* plen doesn't include the length field so need to
* increment by VARHDSZ
*/
pval = (POLYGON *) malloc(plen + VARHDRSZ);
pval->size = plen;
memmove((char *) &pval->npts, PQgetvalue(res, i, p_fnum), plen);
printf("tuple %d: got\n", i);
printf(" i = (%d bytes) %d,\n",
PQgetlength(res, i, i_fnum), *ival);
printf(" d = (%d bytes) %f,\n",
PQgetlength(res, i, d_fnum), *dval);
printf(" p = (%d bytes) %d points \tboundbox = (hi=%f/%f, lo = %f,%f)\n",
PQgetlength(res, i, d_fnum),
pval->npts,
pval->boundbox.xh,
pval->boundbox.yh,
pval->boundbox.xl,
pval->boundbox.yl);
}
PQclear(res);

/* close the cursor */
res = PQexec(conn, "CLOSE mycursor");
PQclear(res);

/* commit the transaction */
res = PQexec(conn, "COMMIT");
PQclear(res);

/* close the connection to the database and cleanup */
PQfinish(conn);

return 0;
}
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原文转自：http://www.ltesting.net