Calling C Numeric Library from Visual Basic and/or Excel

IMSL Library Insight:
Since Visual Basic has become the second most popular programming language behind C, there has been an increased interest in programmers and project managers to call third party technical subroutine libraries from Visual Basic. Visual Basic now comes in several formats including the standard Visual Basic IDE (VB), Visual Basic for Applications (VBA), and VB Script. This makes Visual Basic a language with a large presence in the application development market and one that would benefit from the technical expertise currently available in other libraries. The IMSL libraries, in particular the IMSL C Numerical Library, fits neatly into the category of pre-built technical subroutines that a VB programmer may have a need to access. Generally, these type of routines are very technical and complex making it undesirable to code them from scratch. Calling a standard library of routines makes sense from a time standpoint and in terms of robustness.

Calling the IMSL C Numerical Libraries (CNL) from Visual Basic is largely a matter of addressing the constraints each language places on the mechanism for passing data in and out of subroutines. This includes pointers, differences in the way arrays are stored in each language, and other issues such as optional arguments. The optimal method for addressing these issues is to use an intermediate library written in the native language of the library. Here, data can be converted to the proper types for each language. Optional arguments can also be parsed and the correct calling sequence to the third party routine can then be made. Results from the routine are passed back to the calling program through the same parameter list. In our "VB calling CNL" example, we employ a user-defined model class as the intermediate storage mechanism for receiving data from the VB calling program and for getting data and results from the called CNL function. You should do other house cleaning chores such as checking the IMSL error handler in the intermediate library as well. Errors should be passed back to the VB program either as a global flag or as an extra argument in your VB_to_C_routine parameter list.

Examples of calling the CNL from both Visual Basic/VBA and from inside Excel are available.

Visual Basic Examples (Zip file 152K)

Microsoft Excel Examples (Zip file 457K)