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Programming Interfaces
External Program Interfaces : Shared Library and DLL Support : Passing parameters to a shared library routine : Using MEMPTR variables as parameters : Initializing and uninitializing MEMPTR variables
Initializing and uninitializing MEMPTR variables
Typically when you initialize a MEMPTR variable, you use the SET-SIZE statement to allocate a region of memory for a specified size and associate it with the variable. You can also use a shared library routine to allocate the memory for a MEMPTR variable by passing the variable appropriately as a RETURN parameter to the routine. Then, to complete MEMPTR initialization, you should use the SET-SIZE statement so that ABL knows how big the memory area is.
You must know the exact size of data returned by the shared library routine to initialize the MEMPTR variable properly with the SET-SIZE statement. If you use an incorrect value, you might not be able to access the data as you expect. Note also that if you do not complete initialization of a shared library pre-initialized MEMPTR variable using the SET-SIZE statement, ABL does not perform any bounds checking when you read or modify contents of the structure.
Caution: If you specify a size that is too small, ABL prevents you from accessing parts of the returned structure that lie outside the specified region. However, if you specify a size that is too large (or do not complete initialization at all), you might cause a memory violation by inappropriately accessing memory outside the area of the structure. This can result in loss of data. To determine the size of structures allocated and returned by shared library routines, see the documentation for the routine you are calling.