Question

linux下c++远程连接oracle数据库

最近用c++在做linux下的oracle客户端远程连接数据库开发，遇到一个问题：
我这样定义了一个游标
EXEC SQL declare emp_cursor cursor for select name from admin;
char name[20];
EXEC SQL open emp_cursor ;
EXEC SQL fetch emp_cursor into :name;
从name里面能读到值
但是我想把结果放到一个复合类型里面，然后能按照顺序读
比如
EXEC SQL fetch emp_cursor into 复合类型;
复合类型.get(0)
这些代码我是写在.pc文件里面的，然后用Proc生成.cpp文件再进行编译
我猜想应该是在这里面定义一个复合类型变量
EXEC SQL BEGIN DECLARE SESSION;
//里面定义一个复合类型
EXEC SQL END DECLARE SESSION;
但我不知道怎么写

Answer 1

你说的复合结构应该是结构体吧。 若是 举个例子给你看看 

/*
 *  sample2.pc
 *
 *  This program connects to ORACLE, declares and opens a cursor,
 *  fetches the names, salaries, and commissions of all
 *  salespeople, displays the results, then closes the cursor.
 */
#include <stdio.h>
#include <sqlca.h>
#define UNAME_LEN      20
#define PWD_LEN        40
/*
 * Use the precompiler typedef’ing capability to create
 * null-terminated strings for the authentication host
 * variables. (This isn’t really necessary--plain char *’s
 * does work as well. This is just for illustration.)
 */
typedef char asciiz[PWD_LEN];
EXEC SQL TYPE asciiz IS STRING(PWD_LEN) REFERENCE;
asciiz     username;
asciiz     password;
struct emp_info
{
    asciiz     emp_name;
    float      salary;
    float      commission;
};
/* Declare function to handle unrecoverable errors. */
void sql_error();
main()
{
    struct emp_info *emp_rec_ptr;
/* Allocate memory for emp_info struct. */
    if ((emp_rec_ptr =
        (struct emp_info *) malloc(sizeof(struct emp_info))) == 0)
    {
        fprintf(stderr, "Memory allocation error.\n");
        exit(1);
    }
/* Connect to ORACLE. */
    strcpy(username, "SCOTT");
    strcpy(password, "TIGER");
    EXEC SQL WHENEVER SQLERROR DO sql_error("ORACLE error--");
    EXEC SQL CONNECT :username IDENTIFIED BY :password;
    printf("\nConnected to ORACLE as user: %s\n", username);
/* Declare the cursor. All static SQL explicit cursors
 * contain SELECT commands. ’salespeople’ is a SQL identifier,
 * not a (C) host variable.
 */
    EXEC SQL DECLARE salespeople CURSOR FOR
    SELECT ENAME, SAL, COMM FROM EMP WHERE JOB LIKE ’SALES%’;
/* Open the cursor. */
    EXEC SQL OPEN salespeople;
/* Get ready to print results. */
    printf("\n\nThe company’s salespeople are--\n\n");
    printf("Salesperson   Salary   Commission\n");
    printf("-----------   ------   ----------\n");
/* Loop, fetching all salesperson’s statistics.
  * Cause the program to break the loop when no more
 * data can be retrieved on the cursor.
  */
    EXEC SQL WHENEVER NOT FOUND DO break;
    for (;;)
    {
       EXEC SQL FETCH salespeople INTO :emp_rec_ptr;
       printf("%-11s%9.2f%13.2f\n", emp_rec_ptr->emp_name,emp_rec_ptr->salary, emp_rec_ptr->commission);
    }
/* Close the cursor. */
    EXEC SQL CLOSE salespeople;
    printf("\nArrivederci.\n\n");
    EXEC SQL COMMIT WORK RELEASE;
    exit(0);
}
void sql_error(msg) char *msg;
{
    char err_msg[512];
    int buf_len, msg_len;
    EXEC SQL WHENEVER SQLERROR CONTINUE;
    printf("\n%s\n", msg);
/* Call sqlglm() to get the complete text of the
  * error message.
*/
    buf_len = sizeof (err_msg);
    sqlglm(err_msg, &buf_len, &msg_len);
    printf("%.*s\n", msg_len, err_msg);
    EXEC SQL ROLLBACK RELEASE;
    exit(1);
}

追问

用结构体的话事先得知道查询的字段数吧
我是想把查询做成一个接口
调用接口时sql查询的字段数未知
但是可以通过指定下标来获取该值
比如外部传入的sql语句为select id,name from 表
fetch 到 复合结构
复合结构.get(0)就是id的值
复合结构.get(1)就是name的值
(get方法是我自己臆测的一个获取值的方法，反正就是事先不知道查询的字段数，然后按下标取值)

追答

曾经有看过这样的方法。

用动态查询就可以实现了，不需要知道查询列表项和输入宿主变量的占位符个数
其实使用SQLDA 。

SQLDA就是你所说符合结构
struct SQLDA
{
long N; /* Descriptor size in number of entries */
char **V; /*Ptr to Arr of addresses of main variables */
long *L; /* Ptr to Arr of lengths of buffers */
short *T; /* Ptr to Arr of types of buffers */
short **I; /* Ptr to Arr of addresses of indicator vars */
long F; /* Number of variables found by DESCRIBE */
char **S; /* Ptr to Arr of variable name pointers */
short *M; /* Ptr to Arr of max lengths of var. names */
short *C; /* Ptr to Arr of current lengths of var. names */
char **X; /* Ptr to Arr of ind. var. name pointers */
short *Y; /* Ptr to Arr of max lengths of ind. var. names */
short *Z; /* Ptr to Arr of cur lengths of ind. var. names */
};

实例我没有环境 就不写了。
http://linux.sheup.com/linux/linux4026.htm
方法四
就是你想要的实现方式。

希望对你有帮助

Answer 2

看看c++书再说！