How can I read and write a structure to and from a file?

I'm trying to write a structure to a file, and read that structure in again, possibly with different padding, byte alignment, edianness, and platforms.

fread() and fwrite() don't work when writing the whole structure. Would they work when writing each member of the structure separately?

How could I write a short to a file? Would this work? Would it work only for unsigned shorts?

Code:

---

putc(s/256, fp);
putc(s%256, fp);

---

Can every possible value of a short be written in that way? eg, even ones that would write a '\n' to the file?

Is fwrite()ing a char okay? Even with different edians?

Endian only applies to multi-byte values. Since a char is a single byte, it has no endian.


Quzah.

So the best way to write a short to a file would be something like this?

Code:

---

fwrite(s/256, 1, 1, fp);
fwrite(s%256, 1, 1, fp);

---

Some ideas:
http://c-faq.com/stdio/extconform.html
http://c-faq.com/misc/binaryfiles.html (my first choice)

I would go one of two routes:
a) store the structure as a text file.
b) pack the structure with #pragma's, read each member in individually, and pass to a (conditionally compiled) byte reversal function.

Code:

---

void
convert_to_little_endian(void * ptr, size_t size)
{
#ifdef BIG_ENDIAN_MACHINE
        char
                temp,
                * begin = (char*)ptr,
                * end = begin + size;
               
        while(begin < --end)
        {
                temp = *end;
                *end = *begin;
                *begin++ = temp;
        }
#endif
}

int
main(void)
{
        short
                value;
               
        convert_to_little_endian(&value, sizeof(short));
}

---

Thanks, everyone. I'll see what happens.