Defining Struct Types

A struct type is declared using a labeled DATA block. The label is in the format @STRUCT_NAME where NAME is the name of the struct; e.g. if you’re creating a complex number struct you might write @STRUCT_COMPLEX .

The structure of the DATA block consists of strings in type-name pairs. The end of the definition is notated as DATA "END" .

To continue with our complex number example:


Here, each line is a field declaration. This defines a struct with two floating-point fields: one named REAL and one named IMAGINARY . The valid type indicators are INT for integers, FLOAT for doubles, and STRING for strings.

Creating a Struct

Now that a valid struct has been defined, we can create a variable based on it. The process is simple:


The bare (that is, zero length with no type suffix) array CPX contains the data representing a COMPLEX struct. Now it can be treated and manipluated as a struct using the library. More specifically, it contains the struct type ( COMPLEX ) and data representing all fields ( REAL , IMAGINARY .) This struct is based on the data specified at @STRUCT_COMPLEX . When first created, all fields specify their default value according to type; for INT it is 0, for FLOAT it is 0.0, and for STRING it is the empty string.

Setting and Getting Fields

The method of manipulating fields is rather simple. To set a field’s value, we use SET .


Here the field REAL (specified as a string in the second argument) in CPX is set to 1. The same can be done for all fields and all types of fields without fail. Be wary, however, because due to the lack of proper error handling in SmileBASIC, trying to set a field that doesn’t exist within the struct fails silently.

Getting the value of a field is just as easy. The FIELD function is used to return that field’s value.


Here the value of the field REAL in CPX is obtained and printed. As with SET , this function lacks proper error handling. A nonexistent field will always return 0, regardless of expected type.

Checking Struct Types

To avoid error conditions, the programmer should check struct types for validity when necessary. The main way of doing this is the INSTANCEOF function.


This returns true if STRUCT is an instance of the struct TYPE , otherwise false. This test checks both against the struct’s internal type and its signature (the name and type of its fields.) If these do not match up exactly with a defined struct type then the check is guaranteed false. Improper tampering of the struct’s internal data may cause this check to fail when it otherwise would be guaranteed to pass.

Storing and Loading Structs

A struct can be converted to (and then parsed back out of) a single string. This can be used to keep a collection of structs inside a plain string array, or save a struct to a text file.