Release 10.1A: OpenEdge Development:
Programming Interfaces

Passing CHARACTER values to shared library routines

If you are passing a Progress character string to a shared library routine, you can pass it as a CHARACTER variable or expression. However, if you expect the shared library routine to modify the value, Progress Software recommends that you pass the Progress character string in a MEMPTR memory region as a null-terminated string. This is required if it is an OUTPUT parameter. Otherwise, the shared library routine might inappropriately modify Progress memory outside the bounds of the CHARACTER value with unpredictable results. Assuming Progress has allocated the memory for the string (using SET-SIZE), you then use the GET-STRING function to extract the CHARACTER value.

If the DLL alllocates the memory as either a RETURN value or an OUTPUT parameter, you must use an OUTPUT MEMPTR. For a RETURN parameter, you can use GET-STRING (or another access function) directly on the MEMPTR on return. However, for an OUTPUT parameter, you must use the GET-POINTER-VALUE and SET-POINTER-VALUE functions to access the data on return. (For more information on the GET- and SET-POINTER-VALUE functions, see OpenEdge Development: Progress 4GL Reference .)

The following code fragment shows how to pass an INPUT-OUTPUT string value as a MEMPTR parameter in the case where Progress allocates the memory:

DEFINE VARIABLE MemptrVar AS MEMPTR. DEFINE VARIABLE CharString AS CHARACTER. PROCEDURE DLLfunction EXTERNAL anysystem.dll ORDINAL 10: DEFINE INPUT-OUTPUT PARAMETER StringParm AS MEMPTR. END PROCEDURE. . . . /* The longest string the DLL returns is 256 characters */ len = LENGTH(CharString). siz= (IF len >256 THEN                 len ELSE 256) SET-SIZE(MemptrVar) = siz. PUT-STRING(MemptrVar,1) = CharString. RUN DLLfunction (INPUT-OUTPUT MemptrVar). CharString = GET-STRING(MemptrVar). . . .

The DLL routine is the tenth function in the anysystem.dll file. The SET-SIZE statement allocates to MemptrVar a memory region large enough to hold both the input and output CharString values. The PUT-STRING statement stores the CharString value in MemptrVar. After passing MemptrVar to the DLL routine, the GET-STRING statement returns the (new) value to CharString.