Using ByReference Arguments

When a function accepts a pointer-to-type argument you can use one of the ByReference types to capture the returned value, or subclass your own. For example:

// Original C declaration
void allocate_buffer(char **bufp, int* lenp);

// Equivalent JNA mapping
void allocate_buffer(PointerByReference bufp, IntByReference lenp);

// Usage
PointerByReference pref = new PointerByReference();
IntByReference iref = new IntByReference();
lib.allocate_buffer(pref, iref);
Pointer p = pref.getValue();
byte[] buffer = p.getByteArray(0, iref.getValue());

Alternatively, you could use a Java array with a single element of the desired type, but the ByReference convention better conveys the intent of the code. The Pointer class provides a number of accessor methods in addition to getByteArray() which effectively function as a typecast onto the memory.

Type-safe pointers may be declared by deriving from the PointerType class.