The Venapp development environment provides a flexible way of developing interfaces to simplify access to models. In some cases you may want to have more complete control over your interface and this is possible using the Vensim DLL. The Vensim DLL is a separate program that can be called from other applications such as Visual Basic, Java, Delphi, Excel and multimedia authoring tools. It allows you to make use of the models you have developed in Vensim and, if appropriate, Vensim's tools for analyzing and displaying information. At the same time it allows you to use whatever development and presentation tools you want.
IMPORTANT NOTE Do not ever rename any .dll files or .lib files or they will not work.
The Vensim DLL is not available for the Macintosh.
Functionality
With the Vensim DLL you can display sketches and tool output, setup and perform simulations and manipulate data. Just as for a Venapp, there is no way to build or modify models, but the Vensim DLL does supply some functionality for retrieving information about a model. There are several functions available for interacting with the Vensim DLL but the majority of control will be exercised by passing the Venapp commands to the vensim_command and vensim_tool_command functions. The Vensim DLL can only use packaged models (.vpm files). See "Preparing Models" below.
To use the Vensim DLL, you must create an application in an environment that can call a DLL. This is quite easy to do and there are a number of examples that come with Vensim to demonstrate how this can be done.
Full DLL
The full DLL will allow you to display sketch and graph information (Windows only). Supported commands are documented in a table. Many commands, such as the FILE commands, which will work but are better executed directly from your program. If you try to execute a command that is not supported Vensim will do nothing and return 0.
vensim.ini
The Vensim DLL does not maintain any initialization information from session to session. You can use SETTING> commands to change setting or send the full DLL a SETTING>READINI command if you would like to change settings not available with the SETTING> commands. The Minimal DLL does not support any setting changes.
Redistribution
The Vensim DLL may not be redistributed. User’s of the Vensim Model Reader will have their own copy of the DLL. The Vensim Application Redistribution License does allow for redistribution of a variation of the Vensim DLL.
Distributing Your Work contains more details on redistribution options.
