Re: Back to some basic stuff
"Jack" wrote:
I don't know why I keep getting unresolved external
symbols when I compile this code
You get this error when you link the program rather than
compiling it. Compilation passes without a problem, right?
// File - prochead.cpp
// ...
extern FILE *inFile, *rcFile;
extern struct ResourceTable *pResourceEntry;
// file - ne.cpp
// ...
extern FILE *inFile = NULL;
extern FILE *rcFile = NULL;
extern struct ResourceTable *pResourceEntry = NULL;
Error 1 error LNK2019: unresolved external symbol "struct
ResourceTable * pResourceEntry" ...
The LNK2019 (unresolved external symbol) error means that
linker searched for definition of given symbol across all
modules, but failed to find it (to resolve it).
Given your code, this is no wonder since you don't define
the above variables anywhere. When you specify `extern'
modifier it tells to the compiler: don't search for
definition, it defined elsewhere, let the linker find it
later. That's why the initialization of extern declarations
in "ne.cpp" file dosen't have any effect.
In order to solve it, you need to select one of project
files, where actual definition will be placed. Compiler
independent way to do it is to define a macro:
#if defined(MAIN_UNIT)
# define EXTERN
#else
# define EXTERN extern
#endif // MAIN_UNIT
Then you use `EXTERN' definition everywhere:
// File - prochead.cpp
EXTERN FILE *inFile;
EXTERN FILE *rcFile;
In one (and only) .CPP files define `MAIN_UNIT', so
declarations will omit `extern' modifier:
// file - ne.cpp
#define MAIN_UNIT
EXTERN FILE *inFile;
EXTERN FILE *rcFile;
....
You can save the hustle with a macro by using Microsoft
specific `__declspec( selectany )' modifier everywhere:
__declspec( selectany ) FILE *inFile;
__declspec( selectany ) FILE *rcFile;
Then linker will pick up one of a project files
automatically and put declarations there. Read more info
about `__declspec( selectany )' in MSDN.
HTH
Alex