Portable C code

  • Thread starter Thread starter Kristan Dyson
  • Start date Start date
K

Kristan Dyson

I was just wondering whether you knew whether it is possible to compile a
fully portable C program? I want to write a 'C' CGI program on Windows,
then just upload it to my Plus.Net Debian-based server.
As I want to write pure ANSI C, then I thought it may be possible to write a
program that would run fine on both. Having said that, surely (?), it would
have to be compiled for specific platforms, unless of course there is some
abstraction layer at runtime, like with java. Anyway, this is probably not
possible now I have thought about it.


But I would love to know what you guys and gals think?!



Cheers,

Kristan
 
I was just wondering whether you knew whether it is possible to compile a
fully portable C program? I want to write a 'C' CGI program on Windows,
then just upload it to my Plus.Net Debian-based server.
Click to expand...

Source code is portable. Executables are not. It is quite possible
that an executable on one OS is not recognized as an executable on
another, even if they are running on the actual same CPU (which
dual-boots different OSs). And even if it is, it may not run correctly.
As I want to write pure ANSI C, then I thought it may be possible to write a
program that would run fine on both.
Click to expand...

Compile it on both.
 
[Followups set to comp.lang.c, since I don't suppose the Microsoft people
are all that interested in portability]

Kristan Dyson said:
I was just wondering whether you knew whether it is possible to compile a
fully portable C program?
Click to expand...

That depends on what you mean by "fully portable", of course. But it's
certainly possible to have a very, very portable C program.

What is not possible, alas, is to have one binary that runs on any platform
you like - no matter what language it's written in.

So you do need a compiler on each platform (or group of binary-compatible
platforms) that you wish to support.
I want to write a 'C' CGI program on Windows,
then just upload it to my Plus.Net Debian-based server.
As I want to write pure ANSI C, then I thought it may be possible to write
a program that would run fine on both.
Click to expand...

Well, the point of writing it in pure ANSI C is so that you can compile the
source code without first having to customise it to a particular platform.
 
I was just wondering whether you knew whether it is possible to compile a
fully portable C program? I want to write a 'C' CGI program on Windows,
then just upload it to my Plus.Net Debian-based server.
As I want to write pure ANSI C, then I thought it may be possible to write a
program that would run fine on both. Having said that, surely (?), it would
have to be compiled for specific platforms, unless of course there is some
abstraction layer at runtime, like with java. Anyway, this is probably not
possible now I have thought about it.


But I would love to know what you guys and gals think?!
Click to expand...

You can compile with /Za using Visual C++, that way, any non ANSI code gets
flagged as an error. You should use this if you want to write portable code.

Of course, all compilers (gcc as much as msvc or more) have a lot of
language extensions enabled by default, so doing this on existing code bases
might cause you problems if they use language extensions.
 
Thank you all for your help! Hopefully, I will one day know enough about C
/ C++ to return the favour

cheers
kristan
 
Kristan said:
I was just wondering whether you knew whether it is possible to compile a
fully portable C program? I want to write a 'C' CGI program on Windows,
then just upload it to my Plus.Net Debian-based server.
Click to expand...

You would need to upload the source code and then recompile on the
server to generate new binary executables. If don't have shell access,
or if there is no compiler on the server, you may be screwed.

That's probably one of the things that makes an interpreted language
like Perl more popular for CGI stuff. Install a Windows version of Perl
(ActivePerl ??), monkey with your scripts until they work, then just put
them in proper place on the server.
 
John said:
I don't know much about that
You would need to upload the source code and then recompile on the
server to generate new binary executables. If don't have shell access,
or if there is no compiler on the server, you may be screwed.
Click to expand...
People have told, make the source code portable, binaries are not
portable.
That's probably one of the things that makes an interpreted language
like Perl more popular for CGI stuff. Install a Windows version of Perl
(ActivePerl ??), monkey with your scripts until they work, then just put
them in proper place on the server.
Click to expand...
Perl is good for CGI. So decide early to go for perl/script type
thingies or a full fledged programming language like C.

How to make portable code in C:

1. Have an indepth knowledge of features in ANSI-C. (Not just internals
in C)
2. Study the compilers on platforms you are working in. Different
compilers may or may not support all the features of ANSI-C
3. Try not to use dirty hacks, though great, they are often device
specific
4. Then the lame stuff: design your program logic independent of OS. So
divide device/platform specific code to the logical part of it. e.g.
Don't directly assume fopen would be available created a wrapper for
it.

These are just starters if you are new to making code portable.
 
Kristan Dyson wrote:
Click to expand...
You would need to upload the source code and then recompile on the
server to generate new binary executables. If don't have shell access,
or if there is no compiler on the server, you may be screwed.
Click to expand...

There are cross-compilers available in limited cases.

That's probably one of the things that makes an interpreted language
like Perl more popular for CGI stuff. Install a Windows version of Perl
(ActivePerl ??), monkey with your scripts until they work, then just put
them in proper place on the server.
Click to expand...

No, Perl turns out to relatively *not* portable. For more words
on this subject, please see my earlier posting,
http://groups.google.ca/group/comp.lang.c/msg/044fa97697731535
 
Kristan said:
I was just wondering whether you knew whether it is possible to compile a
fully portable C program? I want to write a 'C' CGI program on Windows,
then just upload it to my Plus.Net Debian-based server.
As I want to write pure ANSI C, then I thought it may be possible to write a
program that would run fine on both. Having said that, surely (?), it would
have to be compiled for specific platforms, unless of course there is some
abstraction layer at runtime, like with java. Anyway, this is probably not
possible now I have thought about it.


But I would love to know what you guys and gals think?!



Cheers,

Kristan
Click to expand...
/* Stirling's approximation for n! & ln(n!) */
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#define PI 3.141592653589793
long double stirling(long double n);
long double lnstirling(long double n);

int main(int argc, char *argv[])
{
long double n, sa, lnsa, pi;

if(argc != 2) exit(EXIT_FAILURE);
pi = PI;
n = strtold(argv[1], NULL);
sa = stirling(n);
lnsa = lnstirling(n);
printf("%.Lf! = %.2Lf\n", n, sa);
printf("ln(%.Lf!) = %.8Lf\n", n, lnsa);

return 0;
}

/* Stirling's approximation */
long double stirling(long double n)
{
long double t1, t2, t3;

t1 = sqrt(2.0 * PI * n);
t2 = pow(n, n);
t3 = exp(-n + 1.0 / 12.0 / n);

return t1 * t2 * t3;
}

/* ln(stirling) */
long double lnstirling(long double n)
{
return (n +.5) * log(n) - n + log(2.0 * PI) / 2.0;
}

*** not part of the program above for Sterlings approximation **

/* Return the natural log of gamma(x) */
double log_gamma(double x)
{
int idx, sizep;
double r, g;
double p[] = {1.000000000190015,
76.18009172947146,
-86.50532032941677,
24.01409824083091,
-1.231739572450155,
1.208650973866179E-3,
-5.395239384953E-6};
r = p[0];
g = 5.;
sizep = sizeof(p) / sizeof(*p);

for (idx = 1; idx < sizep; idx++)
{
r += p[idx] / (x + idx);
}

return log(r) + log(atan(1) * 8) / 2 - log(x) +
log(x + g + .5) * (x + .5) - (x + g + .5);
}
 
quarkLore said:
4. Then the lame stuff: design your program logic independent of OS. So
divide device/platform specific code to the logical part of it. e.g.
Don't directly assume fopen would be available created a wrapper for
it.
Click to expand...
Good point (and very smart design), however do you really think that fopen
should be included in this category? I mean isn't fopen() a part of the C
standard? So it should be in the implementation of every C compiler
 
fopen (standard library) is part of conforming virtual machine. Standard C
allows non-conforming environment, too. Filename format is also
platform-dependent.
 
Alexander Grigoriev said:
fopen (standard library) is part of conforming virtual
machine. Standard C allows non-conforming environment, too. Filename
format is also platform-dependent.
Click to expand...

Please don't top-post. Read these links:
http://www.caliburn.nl/topposting.html
http://www.cpax.org.uk/prg/writings/topposting.php

Standard C doesn't "allow" non-conforming environments, except in the
fairly obvious sense that if an environment doesn't conform to the C
standard, the standard has nothing to say about it.

fopen() is required for all conforming hosted implementations. It's
not required for conforming freestanding implementations (typically
embedded systems). But an implementation that doesn't provide fopen()
likely doesn't have a file system at all.
 
fopen() is required for all conforming hosted implementations. It's
not required for conforming freestanding implementations (typically
embedded systems). But an implementation that doesn't provide fopen()
likely doesn't have a file system at all.
Click to expand...

....or several of them :)
 
Back
Top