SQL/MX Programming Manual for C and COBOL (G06.24+, H06.03+)

Host Variables in C/C++ Programs

HP NonStop SQL/MX Programming Manual for C and COBOL—523627-004

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Using Indicator Variables With the INVOKE Directive

The INVOKE directive automatically generates a two-character indicator variable with

data type short for each host variable that corresponds to a column that allows null.

The name of the indicator variable is the same name as the corresponding column,

plus a suffix and a prefix. If you do not specify a prefix or suffix, the INVOKE statement

appends a default suffix (_i for C) to the indicator variable name.

The format of the indicator variable name depends on the PREFIX, SUFFIX, and NULL

STRUCTURE clauses.

PREFIX and SUFFIX Clauses

The PREFIX and SUFFIX clauses cause the INVOKE statement to generate an

indicator variable name derived from the column name and the prefix or suffix. A

default suffix of _i applies if the INVOKE directive omits these clauses.

Example

The table named c_table has the columns empnum and empname. The column

empname can be null. This example uses an INVOKE statement with both the PREFIX

and SUFFIX clauses:

EXEC SQL BEGIN DECLARE SECTION;

EXEC SQL INVOKE c_table PREFIX beg_ SUFFIX _end;

struct c_table_type mytable;

...

EXEC SQL END DECLARE SECTION;

The SQL C preprocessor generates this structure immediately after the INVOKE

directive in the preprocessed program code:

/* Beginning of generated code for SQL INVOKE */

struct c_table_type {

long empnum;

short beg_empname_end;

char empname[16];

};

In this example, the structure name defaults to the simple name of the table or view

with the suffix _type appended. The structure name is c_table_type.

You must declare a variable of the struct type so that you can use that variable in

your C language statements and your embedded SQL statements. In this example, the

declared struct variable is named mytable.

NULL STRUCTURE Clause

The NULL STRUCTURE clause causes the INVOKE statement to generate a structure

for a column that allows null. It assigns the same name as the column to the structure.

The structure includes fields for the data item, named valu, and its indicator variable,

named indicator.