Preparing the Output XSQLDA to Query Statements with Parameters

Go Up to Method 4: Query Statements With Parameters

Most queries return one or more rows of data, referred to as a select-list. Because the number and kind of items returned are unknown when a statement string is executed, an output XSQLDA must be created to store select-list items that are returned at runtime. To prepare the XSQLDA, follow these steps:

1. Declare a variable to hold the XSQLDA needed to process parameters. For example, the following declaration creates an XSQLDA called ­out_sqlda:

   XSQLDA *out_sqlda;
   

2. Optionally declare a variable for accessing the XSQLVAR structure of the XSQLDA:

   XSQLVAR *var;
   

   Declaring a pointer to the XSQLVAR structure is not necessary, but can simplify referencing the structure in subsequent statements.
3. Allocate memory for the XSQLDA using the XSQLDA_LENGTH macro. The following statement allocates storage for out_sqlda:

   out_sqlda = (XSQLDA *)malloc(XSQLDA_LENGTH(10));
   

   Space for ten XSQLVAR structures is allocated in this statement, enabling the XSQLDA to accommodate up to ten select-list items.
4. Set the version field of the XSQLDA to SQLDA_CURRENT_VERSION, and set the sqln field of the XSQLDA to indicate the number of XSQLVAR structures allocated:

   out_sqlda->version = SQLDA_CURRENT_VERSION;
   out_sqlda->sqln = 10;
   

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