使用带有JNA的TCHAR缓冲区

Question

I am trying to build some Java code to call some networking functions in a DLL written in VC++. The functions exported include (from the .h file)

EX CS BL BOOL CD CsilInit(void);
EX CS BL BOOL CD CsilUnInit(void);
EX CS BL BOOL CD CsilConnect(TCHAR * server, TCHAR * service);
EX CS BL BOOL CD CsilRead(void);
EX CS BL BOOL CD CsilGetData(TCHAR buffer[], int bufflen);

the first 4 of which I have mapped as follows:

boolean CsilInit();
boolean CsilUnInit();
boolean CsilConnect(WString server, WString service);
boolean CsilRead();

All of these seem to be working OK. My problem comes when I try to map the arguments for CsilGetData - the code is presumably expecting a pointer to an array of Unicode characters whose size is defined in the second argument, but I have so far been unable to come up with the correct Java mapping. When called, the buffer will be loaded with data by the native code, and the data will then be read by the calling Java code when the function returns.

Can anyone provide an example of the correct way to do this?

As suggested, I have tried as a test mapping CsilGetData as

boolean CsilGetData(WString buffer, int bufflen)

and then calling it as follows

WString buffer = new WString("               ");
...
while (CSIL.INSTANCE.CsilGetData(buffer, buffer.length())) {
  System.out.print(buffer.toString());
}

but executing the call to CsilGetData gives

Exception in thread "main" java.lang.Error: Invalid memory access at com.sun.jna.Native.invokeInt(Native Method) at com.sun.jna.Function.invoke(Function.java:371) at com.sun.jna.Function.invoke(Function.java:315) at com.sun.jna.Library$Handler.invoke(Library.java:212) at com.sun.proxy.$Proxy0.CsilGetData(Unknown Source) at qeitest.Main.main(Main.java:66)

Technomage suggested using char[] instead, so I revised the code to define the mapping as

boolean CsilGetData(char[] buffer, int bufflen)

and then invoked it as

public static final int cnstBufLen = 2048;
char[] buffer = new char[cnstBufLen];
...
while (CSIL.INSTANCE.CsilGetData(buffer, cnstBufLen)) {
  System.out.print(buffer.toString());
}

but I still get the same Memory Access exception. I believe this is the correct mapping, but I have also tried byte[] with the same result.

Answer 1

Your buffer needs to be writable. String and WString are read-only.

Use char[] for native wchar_t[] and byte[] for native char[] ; you can then use Native.toString() to extract the native NUL-terminated string.