In the C language, strings are stored in arrays of characters. Dynamic statements are constructed in C language strings. These statements can then be executed using the PREPARE and EXECUTE statements. These SQL statements cannot reference host variables in the same manner as static statements since the C language variables are not accessible by name when the C program is executing.
To pass information between the statements and the C language variables, a data structure called the SQL Descriptor Area (SQLDA) is used. This structure is set up for you by the SQL preprocessor if you specify a list of host variables on the EXECUTE statement in the USING clause. These variables correspond by position to place holders in the appropriate positions of the prepared statement.
For information about the SQLDA, see The SQL descriptor area (SQLDA).
A place holder is put in the statement to indicate where host variables are to be accessed. A place holder is either a question mark (?) or a host variable reference as in static statements (a host variable name preceded by a colon). In the latter case, the host variable name used in the actual text of the statement serves only as a place holder indicating a reference to the SQL descriptor area.
A host variable used to pass information to the database is called a bind variable.
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