Do they exist? So far, I only know of fread/fwrite, however the man pages has the following to say about them:
So, do portable binary IO functions exist? Or is their existance fundamentally impossible?Because of possible differences in member length and byte ordering, files written using fwrite() are application-dependent, and possibly cannot be read using fread() by a different application or by the same application on a different processor.
The functions themselves are portable.
What they write is not portable, nor can they ever be.
If you want portable data, then you need to represent it in some other form.
Text is one example.
XDR is another - http://www.faqs.org/rfcs/rfc1014.html
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
If at first you don't succeed, try writing your phone number on the exam paper.
What they are saying is, there is no guarantee that if you read/write data in XYZ format on some platform, you can do the same on another platform. Common example: writing entire structs to a file. The safest way is to format the data yourself in some predefined format before writing, and read the data in that format instead of relying on the system to know what to do.
Code:#include <stdio.h> void J(char*a){int f,i=0,c='1';for(;a[i]!='0';++i)if(i==81){ puts(a);return;}for(;c<='9';++c){for(f=0;f<9;++f)if(a[i-i%27+i%9 /3*3+f/3*9+f%3]==c||a[i%9+f*9]==c||a[i-i%9+f]==c)goto e;a[i]=c;J(a);a[i] ='0';e:;}}int main(int c,char**v){int t=0;if(c>1){for(;v[1][ t];++t);if(t==81){J(v[1]);return 0;}}puts("sudoku [0-9]{81}");return 1;}
Thanks for info guys.
My data scenario is pretty simple, I have a series of strings and integers I need to write to file. The data will be read and written by my app exclusively. I guess what I really need to know is: what is the tolerance between binary code amongst different processors/OS'es. If binary code is not interchangeable between a p3 and p4 and/or between win98 and winXP, then I may have problems, but if its more tolerable, like between an old 386 and a p4 and/or between win95 and winVista , then I won't care as much.
If you're writing out structs, then even just changing the compiler options for the current compiler on the current machine can change the result (eg, packing).
Start changing compilers and machines, and "isCompatible" becomes very fuzzy very quickly.
Stick to text files.
They're very portable, easy to verify, and not really that complicated to parse.
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
If at first you don't succeed, try writing your phone number on the exam paper.
Or you format it specifically, so that say the first 2 bytes contain a number, the next 18 bytes are a string ect... then it would be cross platform compatable, that is how programs like Diablo II do their save files.
And then you have to worry about endianness still.the first 2 bytes contain a number
If you understand what you're doing, you're not learning anything.
Not if you do something like this:
But I think it's a lot easier to just use text.Code:putc(x / 256, fp), putc(x % 256, fp);
dwk
Seek and ye shall find. quaere et invenies.
"Simplicity does not precede complexity, but follows it." -- Alan Perlis
"Testing can only prove the presence of bugs, not their absence." -- Edsger Dijkstra
"The only real mistake is the one from which we learn nothing." -- John Powell
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That's worrying about endiannessOriginally Posted by dwks
The person I was replying to seemed like they were implying you could just do fwrite(&some_short, sizeof(short), 1, fp)
If you understand what you're doing, you're not learning anything.
You can write as a bitstream so that it reads/writes Lo bit to Hi bit. That is worrying about it, but it is the way I have done it and seen it done, just write a class that does your file IO for you, that way you can read/write np.
You're not exactly batting 1.000 today. There are no classes in C.
If you understand what you're doing, you're not learning anything.
whoops forgot this is the C forum heh, you can still write functions to do it for you.
The portable way would be to use XML to put data to files. For simple strings and integers you could just convert all integers to strings, using fprintf() and simmilar functions to write to file.
It is too clear and so it is hard to see.
A dunce once searched for fire with a lighted lantern.
Had he known what fire was,
He could have cooked his rice much sooner.
That's what is meant by "text file". fprintf() instead of fwrite(). 123 instead of #~.
BTW, what XML libraries would you recommend?
dwk
Seek and ye shall find. quaere et invenies.
"Simplicity does not precede complexity, but follows it." -- Alan Perlis
"Testing can only prove the presence of bugs, not their absence." -- Edsger Dijkstra
"The only real mistake is the one from which we learn nothing." -- John Powell
Other boards: DaniWeb, TPS
Unofficial Wiki FAQ: cpwiki.sf.net
My website: http://dwks.theprogrammingsite.com/
Projects: codeform, xuni, atlantis, nort, etc.
Thanks for all the suggestions guys.
What if I were to just export characters/strings only to binary? If I were to just print them byte by byte would I avoid the binary problems associated with multi-byte reading (like with numbers)?
