c - PostgreSQL C API - libq 未定义参考
问题描述
我正在从这里尝试 testPostgreSqlAPI.cpp 示例： http ://www.yolinux.com/TUTORIALS/PostgreSQL-Programming-C-API.html#INSERT_SELECT
我已经在 PostgreSQL 中创建了数据库，我可以看到它是成功的：
bedrock=# SELECT * FROM employee;
idpk | employee_name | dept | jobtitle
------+----------------------+----------------------+----------------------
1 | Fred Flinstone | Worker | Rock Digger
2 | Wilma Flinstone | Finance | Analyst
3 | Barney Rubble | Sales | Neighbor
(3 rows)
bedrock=# \d employee
Table "public.employee"
Column | Type | Collation | Nullable | Default
---------------+---------------+-----------+----------+----------------------------------------
idpk | integer | | not null | nextval('employee_idpk_seq'::regclass)
employee_name | character(20) | | |
dept | character(20) | | |
jobtitle | character(20) | | |
Indexes:
"employee_pkey" PRIMARY KEY, btree (idpk)
但是，当我尝试连接然后使用 testPostgreSqlAPI.cpp 文件从数据库中插入和选择时：
#include <stdio.h>
#include <stdlib.h>
#include </usr/include/postgresql/libpq-fe.h>
/*
* Connect to an existing database.
* Insert a new record for Betty.
* Select full contents of the table and print all fields.
*/
static void
exit_nicely(PGconn *conn, PGresult *res)
{
PQclear(res);
PQfinish(conn);
exit(1);
}
int
main(int argc, char **argv)
{
const char *conninfo = "dbname=bedrock sslmode=disable";
PGconn *conn;
PGresult *res;
int nFields;
int i,
j;
// Make a connection to the database
conn = PQconnectdb(conninfo);
// Check to see that the backend connection was successfully made
if (PQstatus(conn) != CONNECTION_OK)
{
fprintf(stderr, "Connection to database failed: %s", PQerrorMessage(conn));
PQfinish(conn);
exit(1);
}
res = PQexec(conn, "INSERT INTO employee (Employee_Name,Dept,JobTitle) VALUES ('Betty Rubble','IT','Neighbor')");
if (PQresultStatus(res) != PGRES_COMMAND_OK)
{
fprintf(stderr, "INSERT failed: %s", PQerrorMessage(conn));
exit_nicely(conn,res);
}
PQclear(res);
// Use cursor inside a transaction block
// Start a transaction block
res = PQexec(conn, "BEGIN");
if (PQresultStatus(res) != PGRES_COMMAND_OK)
{
fprintf(stderr, "BEGIN command failed: %s", PQerrorMessage(conn));
exit_nicely(conn,res);
}
PQclear(res); // Clear memory
res = PQexec(conn, "DECLARE mydata CURSOR FOR select * from employee");
if (PQresultStatus(res) != PGRES_COMMAND_OK)
{
fprintf(stderr, "DECLARE CURSOR failed: %s", PQerrorMessage(conn));
exit_nicely(conn,res);
}
PQclear(res);
res = PQexec(conn, "FETCH ALL in mydata");
if (PQresultStatus(res) != PGRES_TUPLES_OK)
{
fprintf(stderr, "FETCH ALL failed: %s", PQerrorMessage(conn));
exit_nicely(conn,res);
}
// first, print out the table column attribute names
nFields = PQnfields(res);
for (i = 0; i < nFields; i++)
printf("%-15s", PQfname(res, i));
printf("\n\n");
// next, print out the rows of data
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 portal ... we don't bother to check for errors ...
res = PQexec(conn, "CLOSE mydata");
PQclear(res);
// End the transaction
res = PQexec(conn, "END");
PQclear(res);
// close the connection to the database and cleanup
PQfinish(conn);
return 0;
}
我收到以下错误：
gprbuild -d -P/home/parallels/Documents/C++ Projects/Connecting to a DB/default.gpr /home/parallels/Documents/C++ Projects/Connecting to a DB/src/main.cpp
Link
[link] main.cpp
/home/parallels/opt/GNAT/2020/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.3.1/ld: main.o: in function `exit_nicely(pg_conn*, pg_result*)':
main.cpp:(.text+0x18): undefined reference to `PQclear'
/home/parallels/opt/GNAT/2020/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.3.1/ld: main.cpp:(.text+0x24): undefined reference to `PQfinish'
/home/parallels/opt/GNAT/2020/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.3.1/ld: main.o: in function `main':
main.cpp:(.text+0x51): undefined reference to `PQconnectdb'
/home/parallels/opt/GNAT/2020/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.3.1/ld: main.cpp:(.text+0x61): undefined reference to `PQstatus'
/home/parallels/opt/GNAT/2020/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.3.1/ld: main.cpp:(.text+0x76): undefined reference to `PQerrorMessage'
/home/parallels/opt/GNAT/2020/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.3.1/ld: main.cpp:(.text+0x9e): undefined reference to `PQfinish'
/home/parallels/opt/GNAT/2020/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.3.1/ld: main.cpp:(.text+0xb9): undefined reference to `PQexec'
/home/parallels/opt/GNAT/2020/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.3.1/ld: main.cpp:(.text+0xc9): undefined reference to `PQresultStatus'
/home/parallels/opt/GNAT/2020/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.3.1/ld: main.cpp:(.text+0xdf): undefined reference to `PQerrorMessage'
/home/parallels/opt/GNAT/2020/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.3.1/ld: main.cpp:(.text+0x11a): undefined reference to `PQclear'
/home/parallels/opt/GNAT/2020/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.3.1/ld: main.cpp:(.text+0x12b): undefined reference to `PQexec'
/home/parallels/opt/GNAT/2020/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.3.1/ld: main.cpp:(.text+0x13b): undefined reference to `PQresultStatus'
/home/parallels/opt/GNAT/2020/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.3.1/ld: main.cpp:(.text+0x151): undefined reference to `PQerrorMessage'
/home/parallels/opt/GNAT/2020/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.3.1/ld: main.cpp:(.text+0x18c): undefined reference to `PQclear'
/home/parallels/opt/GNAT/2020/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.3.1/ld: main.cpp:(.text+0x19d): undefined reference to `PQexec'
/home/parallels/opt/GNAT/2020/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.3.1/ld: main.cpp:(.text+0x1ad): undefined reference to `PQresultStatus'
/home/parallels/opt/GNAT/2020/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.3.1/ld: main.cpp:(.text+0x1c3): undefined reference to `PQerrorMessage'
/home/parallels/opt/GNAT/2020/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.3.1/ld: main.cpp:(.text+0x1fe): undefined reference to `PQclear'
/home/parallels/opt/GNAT/2020/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.3.1/ld: main.cpp:(.text+0x20f): undefined reference to `PQexec'
/home/parallels/opt/GNAT/2020/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.3.1/ld: main.cpp:(.text+0x21f): undefined reference to `PQresultStatus'
/home/parallels/opt/GNAT/2020/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.3.1/ld: main.cpp:(.text+0x235): undefined reference to `PQerrorMessage'
/home/parallels/opt/GNAT/2020/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.3.1/ld: main.cpp:(.text+0x270): undefined reference to `PQnfields'
/home/parallels/opt/GNAT/2020/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.3.1/ld: main.cpp:(.text+0x293): undefined reference to `PQfname'
/home/parallels/opt/GNAT/2020/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.3.1/ld: main.cpp:(.text+0x2c8): undefined reference to `PQntuples'
/home/parallels/opt/GNAT/2020/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.3.1/ld: main.cpp:(.text+0x2f5): undefined reference to `PQgetvalue'
/home/parallels/opt/GNAT/2020/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.3.1/ld: main.cpp:(.text+0x329): undefined reference to `PQclear'
/home/parallels/opt/GNAT/2020/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.3.1/ld: main.cpp:(.text+0x33a): undefined reference to `PQexec'
/home/parallels/opt/GNAT/2020/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.3.1/ld: main.cpp:(.text+0x34a): undefined reference to `PQclear'
/home/parallels/opt/GNAT/2020/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.3.1/ld: main.cpp:(.text+0x35b): undefined reference to `PQexec'
/home/parallels/opt/GNAT/2020/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.3.1/ld: main.cpp:(.text+0x36b): undefined reference to `PQclear'
/home/parallels/opt/GNAT/2020/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.3.1/ld: main.cpp:(.text+0x377): undefined reference to `PQfinish'
collect2: error: ld returned 1 exit status
gprbuild: link of main.cpp failed
gprbuild: failed command was: /home/parallels/opt/GNAT/2020/bin/g++ main.o libdefault.a -shared-libgcc -o main
[2020-07-08 10:13:10] process exited with status 4, elapsed time: 01.21s
如果有人能告诉我为什么会这样，将不胜感激。
谢谢
解决方案
您忘记添加告诉ld链接的链接器选项libpq：
-L /path/to/postgresql/lib -l pq
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