[hashcash] Re: hashcash BSD vs GNU getopt bug (Re: documentation bug?)

I often struggle with writing cross platform code. I wonder if anyone
has some good references or resources for this. I want to write command
line code, or libraries suitable for linking with GUI front ends, which
will compile on Linux, BSD, Windows and Macs.

A big help in this direction would be to not even try to support MacOS prior to X (aka "Classic"). OSX and Win32, as well as the more traditional UNIXes, can all use a very similar programming model, with a large enough subset to do most useful things easily. A few macros and a bit of forethought will get you cross-platform and quite complete threading, mutex and network support. The rest can largely be done using the ANSI C library, which is always available.

MacOS Classic's programming model is hugely different, and requires unsubtle hacks at the compiler end even to support the mandatory ANSI C library. If you write a library that doesn't need to use the command line, threading, I/O (including console) or networking at all, however, it should work under Classic as long as you stick to strict ANSI. My fastmint library adheres to this rule as much as possible - except for the GNU assembly which is conditionalised - because it will potentially need to run on all kinds of exotic systems, and particularly Classic.

An alternative is to write in Java, as relatively recent Classic versions have good support for it - but it might give you COBOL fingers. Another alternative might be Python, which can be combined with the wxWindows graphic toolkit. If you must write in C or C++ and need Classic support with a GUI, consider using SDL or a similar cross-platform application framework. GLUT is often unfairly overlooked for this purpose.

One useful piece of information would be symbols which are predefined
by the compiler (or preprocessor), for each architecture, that would
allow you to distinguish them reliably.  I don't know a good source
for this.  I have found that _WIN32 is good for identifying Windows
though.

Look for WIN32, __linux__, __unix__, __MACH__ to distinguish the important platforms, and __GNUC__ to determine whether you're in GCC or not. MacOS X is the one that defines __MACH__ - for some reason it doesn't define __unix__. BSD and Linux should both define __unix__, as should Solaris - on each of these, you can rely on POSIX support, which is much broader than ANSI. If none of the above are present, you're probably compiling for MacOS Classic (or Carbon, which is almost the same), or possibly VMS, or some other exotic system where sticking as close to ANSI as possible is advised.

To get GCC to tell you what it defines by default on a particular machine, use the following:

        $ echo "" | gcc -E -dD - | less

Here's an extract from the output on one of my Linux boxes:

#define __i386 1
#define __i386__ 1
#define i386 1
#define __tune_i586__ 1
#define __tune_pentium__ 1
#define __linux 1
#define __linux__ 1
#define linux 1
#define __unix 1
#define __unix__ 1
#define unix 1
#define __ELF__ 1
#define __gnu_linux__ 1
# 1 "<command line>"
#define __GNUC__ 3
#define __GNUC_MINOR__ 3
#define __GNUC_PATCHLEVEL__ 4
# 1 "<stdin>"

--------------------------------------------------------------
from:     Jonathan "Chromatix" Morton
mail:     chromi@xxxxxxxxxxxxxxxxxxxxx
website:  http://www.chromatix.uklinux.net/
tagline:  The key to knowledge is not to rely on people to teach you it.


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