JNA library

The JNA library (see JNA) is a Java library which allows to interface Java code with C libraries, both for calling C functions from Java or for calling Java methods from the C code.

Overview

Appart from registering the C dlls, the JNA code does not involve any generation of C interface stubs such as JNI. You only have to declare an interface extending the com.sun.jna.Library interface in Java, and call this interface. For example:

      public interface MyCLibrary extends Library {      
        public void myFunction(int value);
      }     

Here if means that there is a function in the C dll called myFunction^[1]

The declspec(dllexport) declaration is there to make the declaration available outside of the dll

:

      declspec(dllexport) void myFunction(int value);

Types correspondance

This paragraph presents the correspondancse between the Java and C types.

Note: Unsigned types use the same mappings as signed types. C enums are usually interchangeable with "int".

Simple types

The table of correspondance for the Java and C simple types is the following:

C type	Java type	Comment	Example
bool	boolean	-	C code: void receive(bool boolValue) Java code: public void receive(boolean boolValue);
char	byte	-	C code: void receive(char cValue) Java code: public void receive(byte cValue);
int	int	-	C code: void receive(int iValue) Java code: public void receive(int iValue);
float	float	-	C code: void receive(float fValue) Java code: public void receive(float fValue);
double	double	-	C code: void receive(double dValue) Java code: public void receive(double dValue);
long	NativeLong	This is the com.sun.jna.NativeLong JNA class	C code: void receive(long lValue) Java code: public void receive(NativeLong lValue);
size_t	long	_	C code: void receive(size_t lValue) Java code: public void receive(long lValue);
char*	String	-	C code: void receive(char* sValue) Java code: public void receive(String sValue);

Structure types

Array types

The table of correspondance for the Java and C simple arrays is the following:

C type	Java type	Comment
bool[]	Pointer	-	C code: void receive(boolean bArray[]) Java code: public void receive(Pointer bArray);
int[dimension]	int[]	-
int[]	Pointer	-	C code: void receive(int iArray[]) Java code: public void receive(Pointer iArray);
float[]	Pointer	-	C code: void receive(float fArray[]) Java code: public void receive(Pointer fArray);
double[]	Pointer	-	C code: void receive(double dArray[]) Java code: public void receive(Pointer dArray);
*char[]	Pointer[]	-