Declare a function implemented in an external library. Note that library and the function implemented in it should be specifically written for ScriptBasic. This command is not able to declare and call just any library function.
The command has three arguments. The argument function is a symbol (a case insensitive string without any space, containing only alphanumeric characters and without double quotes) , the name if the function as it is going to be used in the BASIC program. The BASIC programmer is free to choose this function name. The function later can be used as if it was a BASIC user defined function.
The argument cfun has to be the name of the function as it is defined in the library. This has to be a constant string value. You can not use any expression here but a constant string. This is usually the same as the name of the interface function in the C source file. The programmer writing the module in C has to know this name. If for some reason you do not happen to know it, but you need to declare the function you may be lucky using the name that stands in the C source file between parentheses after the macro besFUNCTION.
The last argument is the name of the library. This also has to be a constant string value. You can not use any expression here but a constant string. This argument has to specify the name of the library file without the extension and the path where the library is located. The extension will automatically be appended to the file name and the path will automatically be prepended to it. The actual extension and the path to be searched for the library is defined in the ScriptBasic configuration file.
You can also specify the full file name containing the full path to the library as well as the file extension. In this case the ScriptBasic configuration file data for the module path and extension is ignored.