Define the SPUPad content

As the first step in creating a SPUPad within your C++ program, identify the types of data that will be saved in your SPUPad. If you plan to have several different types of data in the SPUPad, consider creating a structure type to define the content. (In the SPUPad examples, this structure is called the Root structure type. Each SPUPad gives you access to a portion of memory that can be thought of as the root of a tree. Basically, all the objects in the SPUPad can be reached only through the root object.)

In a root object, you can store a single object (such as int, double), an array (such as char*, int*), or a structure. As an example, assume that you plan to use a SPUPad to store a string of characters. The Root structure might contain a pointer to the string, and perhaps a size value to help set some boundaries for the string size and the memory that is consumed by the SPUPad.

An example of a Root structure for this SPUPad follows:

#include "udxinc.h"
#include <string.h>

using namespace nz::udx;

struct Root
{
 char* data;
 int size;
};

Note: To review the entire sample program and its comments, see The string_pad_create.cpp sample program.

A structure shows an interesting aspect of root objects; for example, the following sample code shows a root object that implements a simple dictionary:

struct MyValue
{
    char* name;
    int value;
};

struct MyLookup
{
    MyValue *values;
    int numallocated;
    int numused;
};

In this example, the root object is an instance of MyLookup, which can contain an arbitrary number of MyValue objects. All of the objects, plus the char* strings, are allocated through the SPUPad allocation mechanisms, but the only way to get to a value (or the name in a value) is through the MyLookup root object.

If you create multiple C++ files to define UDXs that manipulate the data in the same SPUPad, make sure that you repeat your Root structure definition in each C++ file. If you define a number of common structures or definitions, you can create an include file to define all these objects in one location.

Although there is no maximum number of objects that a SPUPad can hold, try to limit the number of objects that you create to only those objects that you really need. The SPUPad tracks each object by using a pointer per object, which adds to the memory consumed by the SPUPad.