语境
我刚刚在 Lion 上安装了 postgres 9.1.4，我想用 C (libpq) 编写一个简单的客户端来连接到 PG 数据库。
psql -l表示postgresDB拥有一个名为mydb的数据库。
psql mydb说：mydb=#
这是尝试连接到 mydb 的小程序：
// Server coordinates
const char * keywords[] = {"dbname", "user", NULL};
const char * values[] = {"mydb", "postgresDB", NULL};
// Check server state
analyse_PQpingParams (PQpingParams (keywords, values, 0));
// Connect to the database
PGconn * conn;
conn = PQconnectdbParams (keywords, values, 0);
// Check if the connection is healthy
analyse_PQstatus (PQstatus (conn));
// Clean exit
PQfinish (conn);
exit (0);
问题
这是程序返回的内容：
analyse_PQpingParams says :
------
The server is running and appears to be accepting connections.
------
analyse_PQstatus says :
------
The state returned was NULL.
------
为什么conn对象为NULL？
文件说什么：
请注意，这些函数将始终返回一个非空对象指针，除非内存太少甚至无法分配 PGconn 对象。如果是内存问题，则psql无法连接到我的数据库。因此，文档在这里没有帮助。也许在其他地方？
非常感谢您的回答！
皮埃尔。
analysis_PQstatus 代码：
void analyse_PQstatus (int status)
{
cout << "\nanalyse_PQstatus says :" << endl;
cout << "------" << endl;
switch (status)
{
case CONNECTION_STARTED:
cout << "Waiting for connection to be made." << endl;
break;
case CONNECTION_MADE:
cout << "Connection OK; waiting to send." << endl;
break;
case CONNECTION_AWAITING_RESPONSE:
cout << "Waiting for a response from the server." << endl;
break;
case CONNECTION_AUTH_OK:
cout << "Received authentication; waiting for backend start-up to finish." << endl;
break;
case CONNECTION_SSL_STARTUP:
cout << "Negotiating SSL encryption." << endl;
break;
case CONNECTION_SETENV:
cout << "Negotiating environment-driven parameter settings." << endl;
break;
case 0 :
cout << "The state returned was NULL" << endl;
break;
default :
cout << "could not analyse this status code : " << status << endl;
}
cout << "------\n" << endl;
}