RE: Getting Started, 'errno' problem

["Colin Peters" <colin at fu dot is dot saga-u dot ac dot jp>]

Stephen E. Schweibinz <plan@mit.edu> wrote:

[snip]
>When I try to run 'make', I keep getting an undefined reference
>to 'errno'.
>
>libpbm.a(libpbm1.o)(.text+0x4e8):libpbm1.c: undefined reference to `errno'
>collect2: ld returned 1 exit status
>make: *** [pbmmerge] Error 1


Have you tried looking at libpbm1.c? Specifically I wonder if perhaps the
file contains code like this:

extern int errno;

/* ... other code ... */

    if (errno == EFOO) /* or something like that */

Basically the problem *might* be that libpbm1.c is assuming that errno is an
ordinary external variable. Unfortunately since errno is in a DLL under
Cygwin32 (IIRC) it isn't, and you have to include errno.h and use the
declaration you get from there (which is probably a macro). This would work
on systems where errno really is just an external int. I have a vague
recollection that the error you get if you include the proper header file
but don't link with libcygwin.a is slightly different, leading underscores
and stuff like that.

This is just a guess.

[snip]
>Including -lc or -lg produces the following error:
>
>C:\Cygnus\B19\H-i386-cygwin32\lib\gcc-lib\i386-cygwin32\
>egcs-2.91.57\..\..\..\..\i386-cygwin32\lib/libcygwin.a(l
>ibccrt0.o)(.data+0x0):libccrt0.cc: multiple definition of
>`_impure_ptr'
>C:\Cygnus\B19\H-i386-cygwin32\lib\gcc-lib\i386-cygwin32\
>egcs-2.91.57\..\..\..\..\i386-cygwin32\lib/libg.a
>(impure.o)(.data+0x2ec):impure.c: first defined here
>collect2: ld returned 1 exit status
>make: *** [pbmmerge] Error 1


Apparently you are linking libcygwin.a, so you don't need to link libc or
libg (I would think).

Colin.

- Colin Peters - colin at fu.is.saga-u.ac.jp
- http://www.geocities.com/Tokyo/Towers/6162/index.html
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