DataBlade® API programming guidelines

The Informix® database server never passes a null-terminated external representation of an mi_lvarchar data type; however, the DataBlade® API provides functions to convert mi_lvarchar values to and from null-terminated strings. To allocate and free memory for mi_lvarchar data types, use the mi_var accessor functions. For more information, see the documentation on the mi_lvarchar_to_string() function in the Informix® DataBlade® API Programmer's Guide.

Opaque data types are wrapped in an mi_lvarchar data type and passed by reference.

Write your user-defined routine code to pass arguments by using a pointer. All built-in data types are passed by reference except fixed-length, noncharacter data types of fewer than 4 bytes. The mi_real data type (the SQL data type SMALLFLOAT) is always passed by reference. Pass opaque data types by value by creating them with the passedbyvalue modifier.

Arguments to C routines cannot be modified unless you specify that the argument is an OUT parameter for a statement local variable. See Informix® User-Defined Routines and Data Types Developer's Guide for more information.

If you create a user-defined routine with the with (handlesnulls) modifier, your routine must check the input parameters to determine if they are null. To check whether arguments are null, pass the MI_FPARAM structure as the last argument in the C routine; then check the arguments by calling the mi_fp_argisnull() function.

If you intend to return a null value from a function, you must call mi_fp_setreturnisnull() with MI_TRUE before the return statement. If you do not, you might receive an incorrect result or memory errors.