Hi, #ifdef ... #define ... #endif protects you from accidently incuding a header file twice in a source file. But since you are including it in different source files, compiler will not complain, but while linking linker will find that 'b' is defined at two places and complain. Can't you use int lawCloseEngine ( int engineID = NONE ) ; I think that should solve your problem. Regards, Cyon P.J. -----Original Message----- From: linux-c-programming-owner@xxxxxxxxxxxxxxx [mailto:linux-c-programming-owner@xxxxxxxxxxxxxxx] On Behalf Of Shriramana Sharma Sent: Saturday, February 24, 2007 9:19 PM To: linux-c-programming@xxxxxxxxxxxxxxx Subject: Multiple declaration problem Hello. I have a problem with multiple declaration in a project I am working on. I have constructed a similar testcase which throws the same kind of error. Please see the files in the attachment. -g or -g3 did not give any useful debugging symbols, I don't know why. The following is the session transcript: $ ls main.cpp myheader.cpp myheader.h $ g++ -c main.cpp $ g++ -c myheader.cpp $ g++ -o main main.o myheader.o myheader.o:(.data+0x0): multiple definition of `b' main.o:(.data+0x0): first defined here collect2: ld returned 1 exit status $ mv main.cpp main.c $ mv myheader.cpp myheader.c $ rm *.o $ gcc -c main.c $ gcc -c myheader.c $ gcc -o main main.o myheader.o myheader.o:(.rodata+0x0): multiple definition of `a' main.o:(.rodata+0x0): first defined here myheader.o:(.data+0x0): multiple definition of `b' main.o:(.data+0x0): first defined here collect2: ld returned 1 exit status In my project, I need to put the following statement in a header file: int lawCurrentEngine = NONE ; // NONE has been enum-med previously because I need to declare a function int lawCloseEngine ( int engineID = lawCurrentEngine ) ; I include the header file containing these two lines in two cpp files, and I get a multiple definition error for lawCurrentEngine just like in the given test case. If I push the lawCurrentEngine declaration to one of the cpp-s (it's not needed in the other cpp) I am unable to provide the default argument for the lawCloseEngine which can be done only in the header. I don't understand how I am getting such an error when I have used the #ifndef #define #endif technique as per good programming practice. Please help, Thanks. Shriramana Sharma. - To unsubscribe from this list: send the line "unsubscribe linux-c-programming" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
