On 30/05/2025 10:20, David Brown wrote:
On 29/05/2025 14:38, Richard Heathfield wrote:
This really is a very simple point, but perhaps a simple analogy
will help to clarify it. You don't throw out your 3/4" just
because you've bought a 19mm. There is room for both in the
toolbox, and why write 3/4" on your new spanner? It /isn't/ a
3/4" spanner even though it's very like it, so why pretend
otherwise?
Your analogy does not cover C99 vs C90.
It does if we can construct a program that is legal C90 but not
legal C99, which is easy enough, or (slightly harder but still not
that hard) a program that is legal in both dialects but which
gives different output under C99 than it does for C90.
$ cat c9099.c; \
gcc -W -Wall -ansi -pedantic -o c90 c9099.c; \
gcc -o c99 c9099.c; \
./c90; \
./c99
#include <stdio.h>
int main(void)
{
int a = 42;
int b = a //* comment */ 6;
;
printf("Soln = %d\n", b);
return 0;
}
Soln = 7
Soln = 42
Obviously it's a contrived example, but then examples pointing out
the consequences of language differences invariably are.
"Lawrence D'Oliveiro" <ldo@nz.invalid> wrote in message news:100jhor$2lgt3$4@dont-email.me...
On Wed, 21 May 2025 10:23:27 +1000, Paul Edwards wrote:...
The C90 standard deferred to MVS - probably still does -
and says that you can't open a file as "w", then read it as
"rb" and write (a new file) as "wb", and still access (the
new file) with "r".
I was shocked when I saw IBM's C library lose the newlines
when I did the above, and went to look at the standard to
show that IBM was violating C90 - but it turns out they
weren't.
That sort of means you can't write a "zip" program portably,
against the theoretical C90 file system. Or you would have
to have flags to say which files need to be opened as text
or binary.
I do not agree with IBM's C library, and PDPCLIB does
not have that behavior, so that constraint could potentially
be dropped in a C90+ standard.
BFN. Paul.
Lawrence D'Oliveiro <ldo@nz.invalid> writes:
On Thu, 22 May 2025 02:20:36 +0200, Jakob Bohm wrote:
The later UNIX-like file system NTFS ...
It was (and is) hard to describe NTFS as “Unix-like”. Yes, it had
hierarchical directories and long(ish) file names, but not much else.
Drive letters were inherited (indirectly) from DEC OSes, of all things,
along with an insistence on having filename extensions, restrictions on
characters allowed in names etc.
I don't believe that NTFS requires filename extensions.
My understanding is that a file name is stored as a single string
(with some restrictions).
Symlinks were not even added until Windows Vista. And you have to have
special privileges to create them.
Do note one more thing.
The C90 standard deferred to MVS - probably still does -
and says that you can't open a file as "w", then read it as
"rb" and write (a new file) as "wb", and still access (the
new file) with "r".
I was shocked when I saw IBM's C library lose the newlines
when I did the above, and went to look at the standard to
show that IBM was violating C90 - but it turns out they
weren't.
That sort of means you can't write a "zip" program portably,
against the theoretical C90 file system.
Or you would have
to have flags to say which files need to be opened as text
or binary.
On 2025-05-21, Paul Edwards <mutazilah@gmail.com> wrote:...
Do note one more thing.
The C90 standard deferred to MVS - probably still does -
and says that you can't open a file as "w", then read it as
"rb" and write (a new file) as "wb", and still access (the
new file) with "r".
You mean:
- write a text file, close it; then
- open it as a binary file and copy the bytes to another, new binary file; and
- finally, read the new binary file in text mode?
I don't see how that would be allowed to lose any newlines.
You made a bitwise copy of the file.
A recent draft of ISO C says "A binary stream is an ordered sequence of characters that can transparently record internal data. Data read in
from a binary stream shall compare equal to the data that were earlier written out to that stream, under the same implementation. Such a stream
may, however, have an implementation- defined number of null characters appended to the end of the stream."
I have C90 somewhere, I can look that up too, but I suspect it was
the same.
I was shocked when I saw IBM's C library lose the newlines
when I did the above, and went to look at the standard to
show that IBM was violating C90 - but it turns out they
weren't.
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