HP NonStop SQL/MP User Manual (English)

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Dynamic SQL Operations

HP NonStop SQL/MP Programming Manual for C—429847-008

10-19

Dynamic Allocation of Memory

provide names for the SQLDA and names buffer as shown:

EXEC SQL INCLUDE SQLDA (dummy_da, 1, dummy_namesbuf, 1);

The INCLUDE directive generates the structure templates sqlda_type and

sqlvar_type, which you can later use to allocate the memory. You might set up

the pointers that will eventually point to that memory. For example:

typedef struct SQLDA_TYPE *sqldaptr;

sqldaptr input_sqlda_ptr, output_sqlda_ptr;

When the memory is allocated, input_sqlda_ptr points to the memory for the

input SQLDA, and output_sqlda_ptr points to the memory for the output

SQLDA. To access the SQLDA and names buffer, declare pointers and then pass

the pointers to a function that allocates the memory as follows:

EXEC SQL BEGIN DECLARE SECTION;

typedef struct SQLDA_TYPE *sqldaptr;

sqldaptr input_sqlda_ptr, output_sqlda_ptr;

typedef char (*arrayptr) [1000];

arrayptr input_namesbuf_ptr, output_namesbuf_ptr;

EXEC SQL END DECLARE SECTION;

To give the DESCRIBE INPUT and DESCRIBE statements a size to use before the

memory is actually allocated, you must declare the names buffer to be an

arbitrarily large size (this example uses 1000). Estimate a number that is greater

than any possible size your names buffer could be. Otherwise, DESCRIBE INPUT

and DESCRIBE might stop describing parameters or variables too soon.

3. Declare an SQLSA structure using the INCLUDE SQLSA directive:

EXEC SQL INCLUDE SQLSA;

4. Dynamically compile the SQL statement (stmt1) entered by the user using the

PREPARE statement as shown in this example:

#define MAX_QUERY_SIZE 512

EXEC SQL BEGIN DECLARE SECTION;

char statement_buffer[MAX_QUERY_SIZE + 1];

...

EXEC SQL END DECLARE SECTION;

...

printf("\nEnter a new SQL statement:\n");

/* Pass statement_buffer to a function that reads */

/* and parses the input (code is in sample program) */

...

EXEC SQL PREPARE stmt1 FROM :statement_buffer;

5. Use the information in the SQLSA structure to determine the number of input

parameters and output variables in the statement.

6. Allocate space for the required number of SQLDA data structures to describe the

parameters and output variables using the malloc function.

7. Allocate space for the values input to the program or output from the database,

again using the malloc function.

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HP NonStop SQL/MP Specifications

General

Platform	HP NonStop Servers
Data Model	Relational
SQL Standard	ANSI SQL
Concurrency Control	Multi-Version Concurrency Control (MVCC)
Fault Tolerance	Yes
High Availability	Yes
Category	Database Software
Initial Release	1980s
Operating System	HP NonStop OS
License	Proprietary
Type	Relational Database Management System
Transaction Management	ACID Compliance
Developer	Hewlett Packard Enterprise