无法使用C ++连接到PostgreSQL [英] Cannot connect to PostgreSQL using C++
问题描述
我试图在我的mac上运行PostgreSQL。 PostgreQL本身工作正常，我可以创建数据库和表和东西，但是当我尝试连接到PostgreSQL使用C ++与类似：
I am trying to run PostgreSQL on my mac. PostgreQL itself works fine and I can create database and table and stuff but when I try to connect to PostgreSQL using C++ with something like:
#include <stdio.h>
#include </Library/PostgreSQL/8.4/include/libpq-fe.h>
#include <string>
int main() {
PGconn *conn;
PGresult *res;
int rec_count;
conn = PQconnectdb("dbname=ljdata host=localhost user=dataman);
if (PQstatus(conn) == CONNECTION_BAD) {
puts("We were unable to connect to the database");
exit(0);
}
res = PQexec(conn, "update people set phonenumber=\'5055559999\' where id=3");
$ b
and compile with something like:
g++ -lpq db.cpp -o db
我得到错误
ld：没有为-lpq
I get the error ld: library not found for -lpq
找到库，如果我编译没有lpq，我得到
and if I compile without lpq, I get
Undefined symbols:
"_PQclear", referenced from:
_main in ccpjNCAU.o
_main in ccpjNCAU.o"
我已经包含libpq-fe.h，应该不会工作？是否有人知道发生了什么问题？
I have already included the libpq-fe.h, shouldn't it work? Does anybody know what went wrong?
推荐答案
g ++找不到 pq library。您必须指定在哪里查找它，资本 -L ：
g++ can't find the pq library. You have to specify where to look for it, with a capital -L:
g++ -L/path/to/pq/lib -lpq db.cpp -o db
pq 是/path/to/pq/lib/libpq.a（或任何扩展名）
where pq is /path/to/pq/lib/libpq.a (or whatever the extension is)
以下是您可能想要执行的操作：
Here's what you probably want to do:
-
将include行更改为不包含路径。
change the include line to not have the path.
#include "libpq-fe.h"
在命令行中添加包含路径
Add the include path to the commandline
g++ -I/Library/PostgreSQL/8.4/include db.cpp
构建中介对象文件
Build intermediary object files
g++ -I/Library/PostgreSQL/8.4/include db.cpp -c -o db.o
将它们作为单独的步骤链接在一起
Link it together as a separate step
g++ -L/Library/PostgreSQL/8.4/lib db.o -lpq
使用 -g
单独构建步骤：编译并链接：
Put it all together, for two separate build steps: compile and link:
g++ -I/Library/PostgreSQL/8.4/include db.cpp -c -g -o db.o
g++ -L/Library/PostgreSQL/8.4/lib db.o -lpq -o db
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