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Asked: 2026-05-18T09:03:21+00:00

I want to include a C library in my Java project via JNI. I

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I want to include a C library in my Java project via JNI. I wrote the necessary JNI wrapper code and I have compiled and tested it in a Linux environment using gcc and make. Now I need to compile this to make a 64 bit Windows DLL, and I cannot get it to compile.

I downloaded Visual C++ Express 2010 and I have been using cl.exe on the command line. In the absence of knowing any better way to do it, I have just called cl.exe with all of the files I want to compile as arguments. I get a variety of errors:

Command line warning D9024: unrecognized source file type 'svm_jni.h'...

and

svm_jni.c(63) : error C2275: 'jobject' : illegal use of this type as an expression...

The first problem I have discovered is do to the fact that cl.exe does not accept .h files (I guess its only meant for C++ instead of C?). Is there a workaround for this? I could change all of the .h files to .c files and change the include statements, but I would prefer not to do this.

I have tried compiling using make and gcc on MinGW, but it always says that it cannot compile to a 64 bit target.

I have tried doing things through VC++ using the makefile project type, but I could not figure out how that works.

Any suggestions?

EDIT: I removed the .h files from the command line arguments and that solves part of the problem. I have been using

-I "C:\Program Files\Java\jdk1.6.0_21\include" -I "C:\Program Files\Java\jdk1.6.0_21\include\win32"

to get jni.h and jni_md.h. I still get

svm_jni.c(63) : error C2275: 'jobject' : illegal use of this type as an expression
    C:\Program Files\Java\jdk1.6.0_21\include\jni.h(83) : see declaration of 'jobject'

and a bunch of syntax and weird errors after that. I am assuming all the errors are the result of a common problem, but I don’t know whats going wrong.

Is there a 64 bit version of jni_md.h? The one I’m using now is in \include\win32

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1 Answer

  1. Editorial Team

    You don’t really want to compile the header files, rather you want to include them in your compilation path when you compile the c/c++ files.

    As for the jobject issue, you need to include the jni header files which are located under the %JAVA_HOME%\include directory.

    For Visual C++ Express, did you download the 64 bit building tools? And when you state that gcc and MinGW cannot compile to a 64 bit target, what message are you getting exactly? Do you have minGW-w64?

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