sqlite3 – 如何在COBOL中编写SQLite回调

我是COBOL程序员,我的最新项目是将COBol应用程序连接到sqlite3数据库.

我一直关注this guide,他们的解决方案正是我在COBol应用程序中所需要的.我已成功设法创建,连接,插入数据和关闭数据库,但当我尝试从数据库中选择数据时出现问题.

在本教程中,他们使用带有双指针的回调.

static int callBACk(void *NotUsed,int argc,char **argv,char **azColName){
   int i;
   for(i=0; i<argc; i++){
      printf("%s = %s\n",azColName[i],argv[i] ? argv[i] : "NulL");
   }
   printf("\n");
   return 0;
}

我在COBol中的解决方案如下

WORKING-STORAGE SECTION.
  *----------------------------------------------------------------*

   01 sqlite3-db         pointer.
   01 err_msg            pointer.
   01 sqlite             pointer.
   01 res                pointer.

   01 notused            pointer.
   01 argc               pic 99 comp-5.
   01 argv               pointer.
   01 azColName          pointer.
   01 Writefunction-Ptr  procedure-pointer.

   procedure division.
          set Writefunction-Ptr to entry "sqlite-callBACk".

          *>Random code.

          call "sqlite3_exec" using
             by value sqlite3-db
             by reference sqlquery
             by value Writefunction-Ptr
             by value 0
             by reference err_msg
           returning rc
          end-call

          *>Random code.

   stop run. 

   entry "sqlite-callBACk" using
           by value notused
           by value argc
           by reference argv
           by reference azColName.

       display argc

       goBACk.
   Entry-Termination.

回调有效,因为它被称为从数据库返回的行数,而整数argc包含表包含的列数.

问题是：

COBol中的双指针,它们是如何表示的？在我的解决方案中,我声明了一个指针,并在指针上使用“by reference”调用回调.不知道这是否是在COBol中表示双指针的正确方法？

如何显示azColName和argv的内容,而不仅仅是指针指向的内存地址？

我现在试图使用SET ADDRESS OF,但我仍然没有让它工作.一定是我错过的东西.我此刻的解决方案如下：

WORKING-STORAGE SECTION.
01 argv pointer.

linkage Section.
01 link-area   pic x.

procedure division using link-area.

 *> RANDOM CODE

     set address of link-area to argv
     call "sqlite3_exec" using
        by value sqlite3-db
        by reference z"SELECT * FROM Cars"
        by value Writefunction-Ptr
        by value 0
        by reference err_msg
        returning rc
      end-call

 *> RANDOM CODE


entry "sqlite-callBACk" using
  by value notused
  by value argc
  by reference argv
  by reference azColName.

  display argc.

  if address of link-area not = null
     display "Contents of new argv: " link-area
  else
     display "empty"
  end-if

  goBACk.

Entry-Termination.

我得到的结果是if语句总是false,因此显示字符串“empty”.但仍然将argc设置为表中的列数.

工作方案：

WORKING-STORAGE SECTION.

   01 argv.
       03  firstcolumn   pointer.
       03  secondcolumn  pointer.
       03  thirdcolumn   pointer.

   01 azColName          pointer.
   01 argc               pic 99 comp-5.
   01 notused            pointer.

   01 Writefunction-Ptr  procedure-pointer.

  *-----------------------------------------------------------------
   linkage Section.

   01 Cars_ID       pic 9(2).
   01 Cars_name     pic X(20).
   01 Cars_Price    pic 9(10).
  /-----------------------------------------------------------------
   procedure division.

    //code      

    set Writefunction-Ptr to entry "sqlite-callBACk".

          initialize sqlquery
          move z"SELECT * FROM Cars;" to sqlquery


          call "sqlite3_exec" using
             by value sqlite3-db
             by reference sqlquery
             by value Writefunction-Ptr
             by value 0
             by reference err_msg
           returning rc
          end-call

    //code

    stop run.



   entry "sqlite-callBACk" using
           by value notused
           by value argc
           by reference argv
           by reference azColName.

       set address of Cars_ID to firstcolumn
       set address of Cars_name to secondcolumn
       set address of Cars_Price to thirdcolumn


       display Cars_ID "|" Cars_name "|" Cars_Price

       goBACk.
   Entry-Termination.