1、远程数据库
设远程数据库的ip地址为192.168.0.1，其中testdb数据库中有student表，student表包含两列：name和age。name为char类型，长度为10；age为int类型，长度为4。
2、源代码
HENV hEnv = NULL; // Env Handle from SQLAllocEnv()
HDBC hDBC = NULL; // Connection handle
RETCODE retcode;
// Allocate memory for ODBC Environment handle
SQLAllocEnv (&hEnv);
// Allocate memory for the connection handle
SQLAllocConnect (hEnv, &hDBC);
// Connect to the data source "test" using userid and password.
SQLCHAR szConnect[] = "DRIVER={SQL Server};SERVER=192.168.0.1;UID=sa;PWD=Goncely;DATABASE=testdb";
SQLCHAR szOutConn[1024];
SQLSMALLINT n(0);
retcode = SQLDriverConnect(hDBC, m_hWnd, szConnect, strlen((char*)szConnect),
szOutConn, 1024, &n, SQL_DRIVER_NOPROMPT);
if (retcode == SQL_SUCCESS || SQL_SUCCESS_WITH_INFO)
{
TRACE("connect to sql server success/n");
HSTMT hStmt = NULL;// Statement handle
// Allocate memory for the statement handle
retcode = SQLAllocStmt (hDBC, &hStmt);
UCHAR szSqlStr[128]= "SELECT * from student" ;
// Prepare the SQL statement by assigning it to the statement handle
retcode = SQLPrepare (hStmt, szSqlStr, sizeof (szSqlStr));
// Execute the SQL statement handle
retcode = SQLExecute (hStmt);
SQLSMALLINT ColumnCount(0);
retcode = SQLNumResultCols(hStmt, &ColumnCount);
TRACE("total %d cols in db./n", ColumnCount);
char name[11];
int age;
SQLINTEGER StrLen_or_Ind;
retcode = SQLBindCol(hStmt, 1, SQL_C_CHAR, name, 24, &StrLen_or_Ind);
retcode = SQLBindCol(hStmt, 2, SQL_C_SLONG, &age, 0, &StrLen_or_Ind);
do
{
retcode = SQLFetch(hStmt);
TRACE("name: %s, age: %d./n", name, age);
}
while(retcode == SQL_SUCCESS);
// Free the allocated statement handle
SQLFreeStmt (hStmt, SQL_DROP);
// Disconnect from datasource
SQLDisconnect(hDBC);
}
else if(/*retcode == SQL_SUCCESS_WITH_INFO ||*/ retcode == SQL_ERROR)
{
TRACE("ai/n");
SQLCHAR Sqlstate[6], MessageText[1024];
SQLINTEGER NativeError;
SQLSMALLINT TextLength;
SQLGetDiagRec(SQL_HANDLE_DBC, hDBC, 1, Sqlstate, &NativeError,
MessageText, 1024, &TextLength);
TRACE("%s/n", MessageText);
}
else
{
TRACE("failed for others/n");
}
// Free the allocated connection handle
SQLFreeConnect(hDBC);
// Free the allocated ODBC environment handle
SQLFreeEnv(hEnv);
3、代码分析
代码以sa账号建立到192.168.0.1服务器中testdb数据库的连接。远程连接的关键函数为SQLDriverConnect，函数的最后一个参数使用了SQL_DRIVER_NOPROMPT，如果将参数改为SQL_DRIVER_PROMPT，则每当此函数被调用后，会弹出一个数据库访问的配置对话框。此对话框的初始信息由szConnect初始化，用户进行更改后，最后的信息会返回到szOutConn，并以此为参数建立远程连接。对于SQL_DRIVER_NOPROMPT标记，函数直接将szConnect的内容拷贝到szOutConn。
成功建立连接后，上述代码的中间部分顺序读取student表中的内容，并trace输出。最后几行代码用于释放资源。
