ALLOCATE DESCRIPTOR Statement [ESQL]

Syntax

ALLOCATE DESCRIPTOR descriptor-name
… [ WITH MAX { integer | host-variable } ]

Parameters

• descriptor-name: – string

  For more information, see Reference: Building Blocks, Tables, and Procedures > SQL Language Elements.

Examples

• Example 1 – This sample program includes an example of ALLOCATE DESCRIPTOR statement usage.

  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  
  
  EXEC SQL INCLUDE SQLCA;
  
  
  #include <sqldef.h>
  
  
  EXEC SQL BEGIN DECLARE SECTION;
  int        x;
  short      type;
  int        numcols;
  char       string[100];
  a_sql_statement_number  stmt = 0; 
  EXEC SQL END DECLARE SECTION;    
  
  int main(int argc, char * argv[])
  {
    struct sqlda *      sqlda1;
  
    if( !db_init( &sqlca ) ) {
        return 1;
    }
  	db_string_connect(&sqlca, "UID=dba;PWD=sql;DBF=d:\\IQ-15_3\\sample.db");
  
    EXEC SQL ALLOCATE DESCRIPTOR sqlda1 WITH MAX 25;
  
    EXEC SQL PREPARE :stmt FROM 
          'select * from Employees';
    EXEC SQL DECLARE curs CURSOR FOR :stmt;
    EXEC SQL OPEN curs;
  
    EXEC SQL DESCRIBE :stmt into sqlda1; 
    EXEC SQL GET DESCRIPTOR sqlda1 :numcols=COUNT; 
        // how many columns?
    if( numcols > 25 ) { 
        // reallocate if necessary
        EXEC SQL DEALLOCATE DESCRIPTOR sqlda1;
        EXEC SQL ALLOCATE DESCRIPTOR sqlda1 
            WITH MAX :numcols;
    }
    type = DT_STRING;   // change the type to string 
    EXEC SQL SET DESCRIPTOR sqlda1 VALUE 2 TYPE = :type;
    fill_sqlda( sqlda1 );  // allocate space for the variables
  
    EXEC SQL FETCH ABSOLUTE 1 curs USING DESCRIPTOR sqlda1;  
    EXEC SQL GET DESCRIPTOR sqlda1 VALUE 2 :string = DATA;
  
    printf("name = %s", string );
  
    EXEC SQL DEALLOCATE DESCRIPTOR sqlda1;
    EXEC SQL CLOSE curs;
    EXEC SQL DROP STATEMENT :stmt;
  
    db_string_disconnect( &sqlca, "" );
    db_fini( &sqlca );
  
    return 0;
  }

Usage

You must declare the following in your C code prior to using this statement:

struct sqlda * descriptor_name

The WITH MAX clause lets you specify the number of variables within the descriptor area. The default size is 1.

You must still call fill_sqlda to allocate space for the actual data items before doing a fetch or any statement that accesses the data within a descriptor area.

Standards