Re: [Mingw-users] Multiple definition error

[Steve P. <st...@ne...>]

A cleaner approach IMHO would be.

utils.h
extern FILE *system_log_file;

utils.c
FILE *system_log_file;

No messy cpp code.

Steve Pribyl
Steve AT NetFuel dot com
Computer Infrastructure Practitioner


Michael Gerdau wrote:
>>    I'm having a problem with a FILE pointer declared inside a header.
>> When I try to link it, i got an "multiple definition" error. Here is a
>> small test case:
> 
> The probelm is you indeed _define_ it twice:
> wherever you include utils.h the filepointer is defined. What you
> actually want to do is define it once and _declare_ it everywhere
> else.
> 
> There are a couple of mechanisms to achieve that:
> 1) Copy the line in utils.h into main.c and change utils.h as follows
>    extern FILE *system_log_file;
> 2) Change utils.h as follows
>    #if defined(IN_MAIN)
>    FILE *system_log_file = NULL;
>    #else
>    extern FILE *system_log_file;
>    #endif
>    and insert
>    #define IN_MAIN
>    in main.c before including utils.h
> 
> There are variations to this but you get the idea.
> 
> HTH, best,
> Michael