The extern statement calls a procedure containing the name and parameter set for a DLL (Dynamic Link Library).
extern procedure, return_value{, parameter_list}
• procedure – The name of the prototype procedure containing the name and parameter set for the DLL. The prototype procedure name must include the name of the function within the DLL, the @ symbol, and be followed by the name of the DLL to be called. This parameter must be enclosed in single quotation marks; it will not compile properly without them.
• return_value – A field that will be set to the value returned by the specified DLL. The control type of this field must match that of the DLL’s return value.
• parameter_list – The list of parameters to be sent to and received from the DLL.
You must create a prototype procedure before you can call a DLL. This is described in Dynamic Link Libraries.