Hi,

I've 2 'C' files in two different folders namely,

/home/data/file1.c
/home/info/file2.c

I've declared a variable in file1.c and I want to use it in file2.c. If I use 'extern' in file2.c 'undefined reference' error gets generated.

How such a variable could be used?

Thanks,
Kranti

Show us how did you compile your code .

I've compiled the code by using 2 different makefiles for those two C files, which contain separate compilation details for respective files.

Moved: This thread is more suitable in Programming, and has been moved accordingly to help your thread/question get the exposure it deserves.

That aside: if you want help, give more detail. doesn't really mean anything to anyone but you.


Cheers,
Tink

Then what did make output?

Such errors occurs at the linking stage, where you need to have the two files (in your case) linked together.

Edit: In simple words it means linking must happen in a common makefile (and using two files).

make gave following results for the code in which i'm making the respective variable extern i.e. "info"

make SPARC=1
/opt/SUNWspro/bin/CC -DSPARC -I../include -I/usr/local/pgsql/include
-I../../include -DDEBUG_ERROR_ENBLED -DDEBUG_WARNING_ENABLED
/opt/SUNWspro/bin/CC -DSPARC -I../include -I/usr/local/pgsql/include
-I../../include -DDEBUG_ERROR_ENBLED -DDEBUG_WARNING_ENABLED
-DDEBUG_NOTICE_ENABLED -DDEBUG_INFO_ENABLED app.c
-o ../../../bin/myApp/sparc/app -lpthread -lsocket
-lnsl
Undefined first referenced
symbol in file
info app.o
ld: fatal: Symbol referencing errors. No output written to
../../../bin/myApp/sparc/app
make: *** [../../../bin/myApp/sparc/app] Error 1

Hi,

Where do you include the object file making up your previously compiled second file (in object format)? It looks like you are just compiling and linking a single file?

You need something like this:
/opt/SUNWspro/bin/CC -c -DSPARC -I../include -I/usr/local/pgsql/include -I../../include -DDEBUG_ERROR_ENBLED -DDEBUG_WARNING_ENABLED file1.c
/opt/SUNWspro/bin/CC -c -DSPARC -I../include -I/usr/local/pgsql/include -I../../include -DDEBUG_ERROR_ENBLED -DDEBUG_WARNING_ENABLED file2.c
/opt/SUNWspro/bin/CC -c -DSPARC -I../include -I/usr/local/pgsql/include -I../../include -DDEBUG_ERROR_ENBLED -DDEBUG_WARNING_ENABLED app.c
/opt/SUNWspro/bin/CC -o ../../../bin/myApp/sparc/app -lpthread -lsocket -lnsl file1.o file2.o app.o

You may have just made a slight error in your extern declaration; is the type the EXACT same as in the real declaration?
ta0kira