[newbie] Which cast to go from *jint to *(unsigned long) ?

[Barth?l?my von Haller]

Hello!

I'm trying to do a c library who will be called from a piece of java
code (JNI). I have the following error when I compile this library :
customJNI.c: In function
`Java_com_xilinx_XHWIF_Boards_custom_customGetSystemInfo':
customJNI.c:55: warning: passing arg 1 of `GetSystemInformation' from
incompatible pointer type

in customJNI.c:55:
result = GetSystemInformation(body, length); // function in custom.c
with jint *body; and jint length;

and in custom.c :
long GetSystemInformation(unsigned long *data, long length) {...}

I understand that GetSystemInformation wait for a pointer unsigned
long and that I give to it an *jint, but I don't know which cast I
must use ?

Thank you, regards

Barthélémy von Haller

 

[xarax]

Hello!

I'm trying to do a c library who will be called from a piece of java
code (JNI). I have the following error when I compile this library :
customJNI.c: In function
`Java_com_xilinx_XHWIF_Boards_custom_customGetSystemInfo':
customJNI.c:55: warning: passing arg 1 of `GetSystemInformation' from
incompatible pointer type

in customJNI.c:55:
result = GetSystemInformation(body, length); // function in custom.c
with jint *body; and jint length;

and in custom.c :
long GetSystemInformation(unsigned long *data, long length) {...}

I understand that GetSystemInformation wait for a pointer unsigned
long and that I give to it an *jint, but I don't know which cast I
must use ?

Thank you, regards

Barthélémy von Haller

Just change your function to:

result = GetSystemInformation((unsigned long*) body, (long) length);

 

[Dan Pop]

Just change your function to:

result = GetSystemInformation((unsigned long*) body, (long) length);

This will shut up the compiler, but it doesn't mean that it is a
particularly brilliant idea, especially if unsigned long and jint
happen to have different sizes.

The OP needs to understand why he is calling GetSystemInformation with
a pointer to jint instead of calling it with a pointer to unsigned long,
as the function expects and change either the caller or the callee so
that they use the same type. The *last* thing you want to do is to
cast a pointer so that the compiler no longer complains about your broken
code.

Dan