thmpsn....@gmail.com a écrit :
On Feb 4, 3:11 am, Bruno Desthuilliers <bruno.
42.desthuilli...@websiteburo.invalid> wrote:
thmpsn....@gmail.com a écrit :
On Feb 3, 1:14 am, David Cournapeau <courn...@gmail.com> wrote:
(snip)
after all, we have used FILE* for years and I have no idea about the FILE
structure.
Your lack of knowledge about it doesn't mean that it has somehow
magically "private" members. The only reason that most of us don't
know what a FILE is is that it's definition is implementation-defined
(i.e., every compiler may define it differently).
That doesn't have anything to do with private members. For example, on
my system, <stdio.h> defines FILE as:
struct _iobuf {
char *_ptr;
int _cnt;
char *_base;
int _flag;
int _file;
int _charbuf;
int _bufsiz;
char *_tmpfname;
};
Didn't you notice kind of a pattern here ?
You mean the leading underscores? I don't think they're used for the
same purpose as in Python.
Not exactly the same purpose, indeed, but there's still something close:
mark the names as "special".
In C/C++, identifiers that begin with an
underscore are reserved (at least at the outer level). Thus, if the
member '_ptr' would instead be named 'ptr', something like this would
break things:
#define ptr // OOPS!!
#include <stdio.h>
That shouldn't happen with '_ptr', since programs are not supposed to
define those kinds of names (yeah, right).
And here again : "would break", "shouldn't", "supposed". Convention over
enforcement.
typedef struct _iobuf FILE;
Given this information, nothing prevents me from writing things like:
FILE* fp = fopen("file.txt", "r");
if (!fp) { /* do something */ }
printf("fp->_cnt = %d\n", fp->cnt);
printf("fp->_flag = %d\n", fp->_flag);
printf("fp->_file = %d\n", fp->_file);
fp->_flag = 0x20; // OOPS!!
>>
Indeed - and that's exactly the point : nothing prevents you from
accessing the implementation, *and yet, you don't*
I sure don't, but I still *can*.
So what ?
CHAOS MAY ENSUE!!
C is not really a new technology, and has been the basis for most
systems for years and years. Looks like nothing that bad as "CHAOS"
really happened so far...
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