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Eli Gottlieb

Operating System Independence

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If I compile code on a non OS-independent compiler, will it still be OS-independent if I didn''t use any system APIs? I really need to know. Thanks in advance. void Signature(void* Pointer) { PObject(Pointer)->ShowMessage("Why do we need so many pointers?"); };

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In theory: yes.

In reality: maybe. It depends. If you don't make any system specific calls (i.e. you don't use conio.h or something like it). For example, the following simple prog should work for any (to my knowledge) OS:


        
#include <iostream>

int main(void)
{
std::cout << "Press enter key to exit...";
std::cin.get();
return(0);
}


However, if you do something like:


       
#include <iostream>
#include <conio.h> // DOS specific


int main(void)
{
std::cout << "Press enter key to exit...";
while(!kbhit()); // also DOS specific

return(0);
}


In general, as long as you avoid OS specific code, you should be ok.


[EDIT] I'll get it right here in second...

/*=========================================*/
/* Chem0sh */
/* Lead Software Engineer & Tech Support */
/* http://www.eFaces.biz */
/*=========================================*/

[edited by - Chem0sh on June 8, 2002 8:17:16 PM]

[edited by - Chem0sh on June 8, 2002 8:17:51 PM]

[edited by - Chem0sh on June 8, 2002 8:18:40 PM]

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Yep. And the reason is simple: YOu do use OS speficic code.

Even when using the non-os-specific libraries, at one point this has to map to functionaltiy in the OS. This is normally deep down in the accompanying .lib files. but these get statically linked into the executable.

And the executable itself will be OS specific - the internal organisation of a windows exe file is different than from it''s Linux or BSD counterpart.

Anyhow, just recompiling is not that complex. BUT you need to keep build environments for everything around. ESPECIALLY because if you talk about a game, there is more than the exe.

That said, STILL stay as far away from things like GCC if you want performing code.

THONA

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quote:
Original post by thona
...Stay as far away from things like GCC if you want performing code.

Excuse you? And use what instead, MSVC? Using GCC makes a lot of sense if you want to develop on multiple platforms, because you''re virtually guaranteed to find GCC for them all (and for free at that), eliminating compiler issues such as standards compliance discrepancies, etc.

I suspect you''re simply ignorant of the -O2 flag.

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A OS-independent compiler is one that can compile for multiple platforms. Also, what is GCC? And I don't have to worry about EXE formats, I know where to find code to parse executable files. OK, here's what an example of what I'm trying to implement. I built a fairly large library in C++ and I compile it into OBJ files without any system calls. Then I write an OBJ file parsing program and use it to link the OBJ files to an application and use them as a library. According to what's been posted here so far, I could compile once and use on any OS where I have a parser becuase there's a standard format for OBJ files. Am I understanding this correctly?

void Signature(void* Pointer)
{
PObject(Pointer)->ShowMessage("Why do we need so many pointers?");
};


[edited by - Eli Gottlieb on June 9, 2002 1:24:25 PM]

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The object code - IIRC - is composed of opcodes. While there''s some similarities between code sets across processors, they''re not all the same. So builing an executable for 80x86 or Pentium will not be able to run on the Motorola (Mac) processors.

Along with that, you''ve got to deal with things like big-endian vs. little-endian... as people have said, the source code would be theoretically fine, but the object code (and therefore the exectuable) would need rebuilding.

OS-Independant compiler: you mean a cross-development system (i.e. developing for Mac on a PC)? As long as the compiler outputs the correct opcodes for the destination processor, it should work fine.

Superpig
- saving pigs from untimely fates
- sleeps in a ham-mock at www.thebinaryrefinery.cjb.net

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quote:
Original post by thona
That said, STILL stay as far away from things like GCC if you want performing code.

I have to agree with Oluseyi on this one. GCC does just fine when you enable optimizations, especially if you hand tune to switches passed to it (or just use -O3 and possibly -funroll-loops).

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quote:
Original post by Null and Void
(or just use -O3 and possibly -funroll-loops).




#
# Optimizations
# -------------

GENERIC_OPT = -O3 -funroll-loops

MIPS_OPT = $(GENERIC_OPT) -INLINE:=ON:all:dfe=ON: -mips4\
-IPA:alias=ON:addressing=ON:aggr_cprop=ON:cgi=ON\
-LNO:auto_dist=ON:non_blocking_loads=ON:gather_scatter=2:ou_further=3:‍Pf1=ON:‍Pf2=ON:‍Pf3=ON:‍Pf4=ON

SPARC_OPT = $(GENERIC_OPT)

X86_OPT = $(GENERIC_OPT)


[edited by - Fruny on June 9, 2002 2:48:40 PM]

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