Re: gcc compile options

[pkurpis@keck.hawaii.edu (Peter Kurpis)]

> have to do the following: compile multi-thread C++
> programs, generate an executable file and create a
> shared library with a list of exported external
> symbols of the shared object files. I need to do that
> in three distinct steps since I have to use a make
> file previously developed for use on AIX (VisualAge
> C++ compiler).
> 
> I'm thiinking of using the folowing commands
> ("make-like") to compile and create an executable
> file, but I don't know how to create shared libraries
> and export the symbols...
> 
> compile:
> gcc -x c++ -g -Iincdir -c srcdir/*.c objdir/*.o
> -mthreads

Use  g++  to compile c++ code, not  gcc -x c++ .  Also,
you need to use  -o  to specify the output file.

If you are writing a makefile, I would guess you just
need to specify the standard make variables, e.g.

CXX = g++
CPPFLAGS = -g -Iincdir

and use make's implicit rule for .cc files.

> create the executable:
> gcc -lsomelib -o execfile objfiles

The order of libs and objfiles matters, as the linker
only makes one pass through the command line resolving
symbols.  Ordinarily, libs resolve symbols in your
objfiles, so

g++ -o execfile objfiles -lsomelib

Note again the use of g++.  It has knowledge of what to
link against implicitly, a different set of things than 
gcc.

To create a shared library, since you are using the GNU
ld (inherently configured into gcc):

g++ -shared -o sharedlib objfiles

I haven't looked up whether you can create a list of 
exported symbols at link time -- you probably can, and 
you can pass the option to  ld  via
 -Wl,-xxx  where  xxx  is the option string.  (See  man ld
for the right thing.)  Alternatively, you can use  nm  
and  grep  to do the same thing.