g++ linking

[jamesedwards]

Hello,

I have my two main files:

main.h

#include <jni.h>
// Load libs
#ifdef DARWIN // MacOSX
#include "os/darwin/darwin_os.h"
#elif LINUX // Linux
#include "os/linux/linux_os.h";
#endif // End

main .cpp

.... (JNIEnv *env, jobject jobj) {
// idea being that depending on the header loaded it will return the cpu load depending on the OS.
return cpu();
}

linux_os.h

....

linux_os.cpp

double cpu() {
return 23.3;
}

I am currently,

g++ -Wall -c os/linux/linux_os.cpp

then,

g++ -Wall -fPIC -shared -I /usr/lib/jvm/java-1.6.0-openjdk-1.6.0.0/include -I /usr/lib/jvm/java-1.6.0-openjdk-1.6.0.0/include/linux/ linux_os.o -c main.cpp

which returns

error: ‘cpu’ was not declared in this scope

I am clearly missing something with linking the libraries. Help is greatly appreciated. Thanks.

[GNU-Fan]

Just what the compiler says.

cpu isn't declared when compiling main.cpp.
You resolve this by putting a function prototype in linux_os.h and #include it in main.cpp.

I am clearly missing something with linking the libraries.

No. If you use the -c option or there was a problem with compiling, you don't get to the linking stage.

[jamesedwards]

Hello,

Thank you for your reply, the g++ is now working fine. However the complier is throwing out:

g++: linux_os.o: linker input file unused because linking not done

Any ideas? Thanks.

P.s. I have read the thread to do with this error already posted on this forum.