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Re: portable code

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rangsynth@gmail.com writes:
> You can say 
>
>   write((i >> 24) & 0xFF)
>   write((i >> 16) & 0xFF)
>   write((i >> 8) & 0xFF)
>   write(i & 0xFF)

There is no write() in C, but there is one in POSIX that doesn't match
this usage:

    ssize_t write(int fd, void *buf, size_t len);

Let's assume for now that this in fact a private function based on
a global FILE *f:

void write(unsigned char i)
{
    if (fwrite(&i, 1, 1, f) != 1) {
        fprintf(stderr, "fwrite() failed\n");
        exit(EX_FAILURE);
    }
}

(actually, we should assume that this function is called funwrite() and
that write() is the following macro:

#define write(i) funwrite(i);

but I'm being charitable)

>   int out = 0;
>   out += (read() >> 24);
>   out += (read() >> 16);
>   out += (read() >> 8);
>   out += (read());

There is no read() in C, but there is one in POSIX that doesn't match
this usage:

    ssize_t read(int fd, void *buf, size_t len);

Let's assume for now that this is in fact a private function based on a
global FILE *f:

unsigned char read(void)
{
    unsigned char i;
    if (fread(&i, 1, 1, f) != 1) {
        fprintf(stderr, "fread() failed\n");
        exit(EX_FAILURE);
    }
    return i;
}

then the following:

    unsigned int i = 0x01020304;
    write((i >> 24) & 0xFF);
    write((i >> 16) & 0xFF);
    write((i >> 8) & 0xFF);
    write(i & 0xFF);
    rewind(f);
    i = 0;
    i += (read() >> 24);
    i += (read() >> 16);
    i += (read() >> 8);
    i += (read());
    printf("i = 0x%x\n", i);

will print

    i = 0x4

The correct answer is "store your data in a textual representation".

DES
-- 
Dag-Erling Smørgrav - des@des.no
-- 
comp.lang.c.moderated - moderation address: clcm@plethora.net -- you must
have an appropriate newsgroups line in your header for your mail to be seen,
or the newsgroup name in square brackets in the subject line.  Sorry.

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Thread

Re: portable code rangsynth@gmail.com - 2012-04-04 18:05 -0500
  Re: portable code Dag-Erling Smørgrav <des@des.no> - 2012-04-23 08:31 -0500
    Re: portable code Jorgen Grahn <grahn+nntp@snipabacken.se> - 2012-04-30 21:59 -0500
      Re: portable code Dag-Erling Smørgrav <des@des.no> - 2012-05-04 17:29 -0500
        Re: portable code Jorgen Grahn <grahn+nntp@snipabacken.se> - 2012-05-09 01:06 -0500
    Re: portable code Jiří Zárevúcky <zarevucky.jiri@gmail.com> - 2012-05-04 17:30 -0500

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